Since PHP doesn't have a nice snmptable-like function... here is a quick-and-dirty hack that works for me. Works on complete and sparse tables. The example oids are for the route (complete) and interface (often sparse) tables.

<?php
    $a = snmptable("10.1.1.1", "public", ".1.3.6.1.2.1.4.21") or die("error");
    print_r($a);
    $a = snmptable("10.1.1.1", "public", ".1.3.6.1.2.1.2.2") or die("error");
    print_r($a);

function snmptable($host, $community, $oid) {
    // TODO: get original state and restore at bottom
    snmp_set_oid_numeric_print(TRUE);
    snmp_set_quick_print(TRUE);
    snmp_set_enum_print(TRUE); 

    $retval = array();
    $raw = snmprealwalk($host, $community, $oid) or die("snmptable: unable to walk OID $oid");

    $prefix_length = 0; 

    foreach ($raw as $key => $value) {
        if ($prefix_length == 0) {
            // don't just use $oid's length since it may be non-numeric
            $prefix_elements = count(explode('.',$oid));
            $tmp = '.' . strtok($key, '.');
            while ($prefix_elements > 1) {
                $tmp .= '.' . strtok('.');
                $prefix_elements--;
            }
            $tmp .= '.';
            $prefix_length = strlen($tmp);
        }
        $key = substr($key, $prefix_length);
        $index = explode('.', $key, 2);
        isset($retval[$index[1]]) or $retval[$index[1]] = array();
        isset($firstrow) or $firstrow = $index[1];
        $retval[$index[1]][$index[0]] = $value;
    }

    // check for holes in the table and fill them in
    foreach ($retval[$firstrow] as $key => $tmp) {
        foreach($retval as $check => $tmp2) {
            if (! isset($retval[$check][$key])) {
                $retval[$check][$key] = '';
            }
        }
    }

    return($retval);
}
?>

To check if there were any results found you have to use the empty() function.  The count() function always returns a number 1 or larger.

     $walk_result = snmprealwalk($machine_ip, $community, $snmpcodes['interface_names']);

    if (empty($walk_result)) {
        print "No network interfaces found.<br>\n";
        exit(0);
    }

Here's a way to find the uptime and number of users on a machine. (Note that uptime is the uptime of the snmpd daemon, which should be fairly close to the uptime for the host.)

<?php
        $state = snmprealwalk($host, "public", ".1.3.6.1.2.1.25.1", 50, 1);
        $uptime = ereg_replace("^.*\) ([0-9]+ .*):[0-9][0-9]\.[0-9]{2}.*$", "\\1", $state['host.hrSystem.hrSystemUptime.0']);
        $users  = (int)ereg_replace("Gauge32: ", "", $state['host.hrSystem.hrSystemNumUsers.0']);
        printf('<div class="machine"><dt>%s</dt><dd>%s</dd>', $host, $desc);
        printf('<dd>up %s</dd>', $uptime);
        if ( $users ) printf('<dd>%d user%s</dd>', $users, ($users > 1) ? 's' : '');
        printf('</div>');
?>

snmprealwalk indexes the values using the oid instead of an integer. This is useful when you need data that is contained in the oid as well as the value. 

Here's an example for retrieving and printing vlan info:
//
// I have collected the vlan identifiers earlier from the 3com mib and they are stored in the $vlan table.
// 
  for($n=0;$n<count($vlan);$n++){
    print $vlan[$n][id]."  ".$vlan[$n][name]."<br>\n";
    $ifStackStatusTable=@snmprealwalk($switch, $community, ".1.3.6.1.2.1.31.1.2.1.3.".$vlan[$n][id]); // ifMIB.ifMIBObjects.ifStackTable.ifStackEntry.ifStackStatus
    for(reset($ifStackStatusTable);  $port = key($ifStackStatusTable);  next($ifStackStatusTable)){
      print "$port=$ifStackStatusTable[$port]<br>";
      }

If you wish to use version 2c or 3, use the following functions:

snmp v2c functions:

snmp2_get (string host, string community, string object_id [, int timeout [, int retries]])
snmp2_getnext (string host, string community, string object_id [, int timeout [, int retries]])
snmp2_walk (string host, string community, string object_id [, int timeout [, int retries]])
snmp2_real_walk (string host, string community, string object_id [, int timeout [, int retries]])
snmp2_set (string host, string community, string object_id, string type, mixed value [, int timeout [, int retries]])

snmp v3 functions:

snmp3_get (string host, string sec_name, string sec_level, string auth_protocol, string auth_passphrase, string priv_pr)
snmp3_getnext (string host, string sec_name, string sec_level, string auth_protocol, string auth_passphrase, string pri)
snmp3_walk (string host, string sec_name, string sec_level, string auth_protocol, string auth_passphrase, string priv_p)
snmp3_real_walk (string host, string sec_name, string sec_level, string auth_protocol, string auth_passphrase, string p)
snmp3_set (string host, string sec_name, string sec_level, string auth_protocol, string auth_passphrase, string priv_pr)

Attention: timeout is in microseconds (multiply by 1,000,000 for seconds)

Some improvements based on testing a lot of OIDs on a lot of devices.

<?php
function snmptable($host, $community, $oid) {
    // TODO: get original state and restore at bottom
    snmp_set_oid_numeric_print(TRUE);
    snmp_set_quick_print(TRUE);
    snmp_set_enum_print(TRUE); 

    $retval = array();
    $raw = snmprealwalk($host, $community, $oid);
    if (count($raw) == 0) return ($retval); // no data
    
    $prefix_length = 0; 
    $largest = 0;
    foreach ($raw as $key => $value) {
        if ($prefix_length == 0) {
            // don't just use $oid's length since it may be non-numeric
            $prefix_elements = count(explode('.',$oid));
            $tmp = '.' . strtok($key, '.');
            while ($prefix_elements > 1) {
                $tmp .= '.' . strtok('.');
                $prefix_elements--;
            }
            $tmp .= '.';
            $prefix_length = strlen($tmp);
        }
        $key = substr($key, $prefix_length);
        $index = explode('.', $key, 2);
        isset($retval[$index[1]]) or $retval[$index[1]] = array();
        if ($largest < $index[0]) $largest = $index[0];
        $retval[$index[1]][$index[0]] = $value;
    }

    if (count($retval) == 0) return ($retval); // no data

    // fill in holes and blanks the agent may "give" you
    foreach($retval as $k => $x) {
        for ($i = 1; $i <= $largest; $i++) {
        if (! isset($retval[$k][$i])) {
                $retval[$k][$i] = '';
            }
        }
        ksort($retval[$k]);
    }
    return($retval);
}
 ?>