From PostgreSQL wiki
vTiger CRM version 4.2.4 works with Postgres. It can be downloaded here
Note that this version is from June 07, 2005 - the vTiger project had a sub-project to implement PG support in their 5.0x versions; they project having it available in 5.0.3 or 5.0.4. Note that 5.0.3 has been in "RC2" status for a very long time now.
vTiger is a fork of SugarCRM with some nice additions; if you don't mind using software for which you can't get any form of support (the forums are unresponsive for old versions), and you have time to test for your environment (load testing, etc), then I highly recommend this product.