I'm 99% sure your problem is that your new router uses a different default subnet. For example, Netgear routers use a default of 192.168.0.x while Linksys routers use 192.168.1.x. So if your PS2's IPCONFIG.DAT is 192.168.0.10 and you connected a Linksys or some other router whose default network is 192.168.1.x then your machines won't see each other.
The easiest solution if this is the case would be to enter your router config and change your default addressing scheme to match the one your old router had. Then you wouldn't need to change any of your stuff on the PS2 side.
Note: If you change the address scheme in your router, you'll need to renew your IP address on your computer because you will temporarily lose connectivity. Just go to a command prompt and type ipconfig/renew.