Wired and wireless

Question, got a wireless router, laptop, and desktop pc. Desktop is connected to internet via ethernet cable, no wireless card installed. Laptop is a macbook and works fine on wireless to get to internet. However they cannot see each other on my network. As in the laptop cannot ping the pc successfully, but the desktop can ping the laptop. So it's like the laptop just can't see the desktop. Anyway to fix this, or do I need to get a wireless card for the desktop? Btw, wouldn't be too concerned if my network went all wireless as I'm running WPA security, with 64 character length HEX password, and can enable MAC address filtering, as well as running software fiewall on the desktop.

No, b/c I also tried turning the firewall off, at least I'm fairly certain, and I don't think the windows firewall was enabled either.

wrong, the MAC book needs to turn on Windows sharing and Personal file sharing checked off in system preferences/sharing. When done sharing it will ask a name for windows sharing, give the name of the windows PC. Then share the files on the windows machine. This is al you should have to do, this is what I did and it took 5 minutes.