If your new homebuilt pc has Wifi or a wifi dongle then probably, yes. You would have to be within range of the laptop, and your computer would need setting up with wireless networks.
If it's a homebuilt PC, you'd probably know about it. If you are using Windows XP, you can check by going Start > Settings > Network Connections (in classic start menu) and wireless connection would show up under there.
Something like this would give your computer WiFi. Also this would give you Wifi, but it connects via USB and can be removed and put into other computers easier.