PokerTracker

I note that PT3 looks like it is x32 only. Does this mean it has a max.4gig limit?

What about Postgress x64 v.9. That supports obv more memory but can Pokertracker use it?

I now have 32gig in my PC...

PT3 itself can only use 2GB as it is a 32-bit process.
If you have a 64-bit version of PostgreSQL it should be able to use more of your RAM. That isn't part of PT3 - PT3 uses the PostgreSQL service, but it runs independently of PT3 and manages its own memory etc.