Important: In order to use the UCD SNMP package, you need to define
  NO_ZEROLENGTH_COMMUNITY to 1 before 
  compiling it. After configuring UCD SNMP, edit config.h 
  or acconfig.h and search for
  NO_ZEROLENGTH_COMMUNITY. Uncomment the #define line. It 
  should look like this afterwards:
  
| #define NO_ZEROLENGTH_COMMUNITY 1 | 
  Now compile PHP 
--with-snmp[=DIR].
 
  If you see strange segmentation faults in combination with SNMP commands,
  you did not follow the above instructions. If you do not want to recompile
  UCD SNMP, you can compile PHP with the 
  --enable-ucd-snmp-hack switch which
  will work around the misfeature.
 
  The Windows distribution contains support files for SNMP in the
  mibs directory. This directory
  should be moved to DRIVE:\usr\mibs,
  where DRIVE must be replaced with the driveletter where PHP is installed on,
  e.g.c:\usr\mibs.