I have 2 Cisco PIX 525 Firewalls and I don't have any router.
They are running version 7.2.
Can i use that as a Layer 3 router and use its interfaces for different subnets?
In the immortal words of Cisco (circa 1999), "the PIX is a firewall, not a router"
That said, it can be used as a router. But you're better off using anything else, as it's firewall nature is going to be a pain in the ass. (I used to do it with a PIX 520, and I hated it for all time.) If it's what you have, then it's all you have, but I cannot over emphasize how much better off you'll be with an actual router. (buy one, build one, whatever it takes.)