Transfer files on LAN...between 2 PCs

Ok so I have two PCs at home, one (that i’m using now) is downstairs plugged into my Netgear router via ethernet cable and the other connects fo the router wirelessly…

I’v been trying to browse the files on the upstairs computer from the downstairs one…how can I get it to work?

I have a PowerBook G4 that also connects to the network, I can connect to it by using SmartFTP and typing in it’s IP address (allowing me to browse the HD and move files back and foward).

How can I get a similar thing going for my PCs, they both have XP (one is Home edition and one is Pro).

I tried that Hamatachi or whatever it’s called but it didn’t work…