You can get some possibly more useful information with the query:

SELECT table_name, column_name, data_type, character_maximum_length FROM information_schema.columns WHERE table_name='tablename';

If parameter $extended not false:
<?php
array (size=2)
  'name' => 
    array (size=11)
      'num' => int 1
      'type' => string 'varchar' (length=7)
      'len' => int -1
      'not null' => boolean false
      'has default' => boolean true
      'array dims' => int 0
      'is enum' => boolean false
      'is base' => boolean true
      'is composite' => boolean false
      'is pesudo' => boolean false
      'description' => string '' (length=0)
  'id' => 
    array (size=11)
      'num' => int 2
      'type' => string 'int4' (length=4)
      'len' => int 4
      'not null' => boolean true
      'has default' => boolean true
      'array dims' => int 0
      'is enum' => boolean false
      'is base' => boolean true
      'is composite' => boolean false
      'is pesudo' => boolean false
      'description' => string '' (length=0)
?>

To specify a schema as well as a table name, use the "schemaname.tablename" form as usual for PostgreSQL and the other functions in this extension. Without the prefix, of course, the default schema search path is used.

<?php
  $meta = pg_meta_data($dbconn, 'foo.bar'); // table "bar" in schema "foo"
  if (is_array($meta)) {
      var_dump($meta);
  }
?>

This function seems to be case-sensitive on tablename (php-4.3.1)

The Array returned is of the following structure
['field name'] => Array
   (
     ['num'] => Field number starting at 1
     ['type'] => data type, eg varchar, int4
     ['len'] => internal storage size of field. -1 for varying
     ['not null'] => boolean
     ['has default'] => boolean
   )
     ......

for Varied size datatypes (varchar, text, etc) 
you can get the max data length from the system table pg_attribute.atttypmod -4
eg. 
select attnum, attname , atttypmod -4 as field_len 
from pg_attribute, pg_class 
where relname='$tablename' 
and attrelid=relfilenode 
and attnum>=1

When querying on meta data from a temp table, the meta data seems to persist even if a fresh connection is established, where the temp table no longer exists.

 For example, if you create a connection and a temp table like so:
$dbconn1 = pg_connect('blah blah', , PGSQL_CONNECT_FORCE_NEW);
pg_exec($dbconn1,'create temp table foo as select 'foo' as namecol, 'bar' as valcol');

Then create a new connection

$dbconn2 = pg_connect('blah blah', , PGSQL_CONNECT_FORCE_NEW);

And query the meta data for table 'foo' in this new connection, it will report the facts about this table:
pg_meta_data($dbconn2,'foo');

"'Array ( [foo] => Array ( [num] => 1 [type] => varchar... "

However, trying to remove this table:
pg_exec($dbconn,'drop table foo');

Throws an error:
pg_exec(): Query failed: ERROR: table "foo" does not exist in ...

The built in function does not provide any support for selecting a schema.  If you need schema support and do not want to alter your SEARCH_PATH, the following function can provide it:

 function meta_data($table, $schema = 'public')
    {
$result = pg_query_params("SELECT a.attname, a.attnum, t.typname, a.attlen, a.attnotNULL, a.atthasdef, a.attndims 
FROM pg_class as c, pg_attribute a, pg_type t, pg_namespace n
WHERE a.attnum > 0 
AND a.attrelid = c.oid 
AND c.relname = $1
AND a.atttypid = t.oid 
AND n.oid = c.relnamespace
AND n.nspname = $2
ORDER BY a.attnum", array($table, $schema));
$fields = array();
while($row = pg_fetch_array()) {
$fields['attname'] = $row;
} 
        return $fields;
    }