I've not used it but Buchan has some fairly explicit instructions as comments at the top of the script. If you're using newer Xymon, you might just have to translate some of the file names to what they are now. Should be fairly straightforward.
=G=
From: xymon-bounces at xymon.com [xymon-bounces at xymon.com] on behalf of Lucas Wang [user-0fbbd87b09cf@xymon.invalid]
Sent: Tuesday, March 26, 2013 9:56 AM
To: xymon at xymon.com
Subject: [Xymon] using external script to monitor ldap
Is there anyone monitor Ldap server using attached perl script? Can you please share the detail of how the use this script?