Need help connecting to home Mac!

Hi, I am trying to connect to my home computer from my work computer, but I am not able to connect to it. I do CMD+K (from work) and type in the IP address (with & without smb:// &/or afp://), but home computer does not show up or the connection times out. My home computer is awake and file sharing & remote login are on. My home computer is an Imac 20" Intel Core 2 Duo connected via cable modem @ 12mbps running 10.5.2. My work computer is a Power Mac G5 Duel 2.7 running 10.4.11. Am I not able to connect because of the OS difference? Any help would be appreciated.
p.s. Sorry if this is a repost, but I couldn't find any posts with questions like this. Thanks.

damn...maybe that's it. My default OSX firewall is probably on. I suppose I'll check that, since I have no other firewall anywhere. Thanks.

I just checked and my firewall was off, so no firewall and in response to the previous post, I only have a ethernet hub splitting my cable modem to my PC/PS3/Mac. The PC & PS3 have no problem seeing the Mac. Thanks.