Hi, jwenting: There are some less expensive paths to take than mine. For example if you existing desktop PC running Microsoft Windows or Linux uses a USB keyboard and mouse, you can opt to use a USB KVM. I saw one at the local Apple Store that also switches the audio/speaker. But, every Mac expert I've heard or read advices to bump the RAM up to at least 512MB. If you plug your Mac mini into a wired LAN (instead of my 802.11g route), you can save up to $100 there too.
You might want to take a look at the iBook G4 with 12" LCD. I'm amazed by its battery life. On the WinTel, side, the new Dell Lattitude X1 looks very nice at 2.5 lbs.