I sometimes run Garmin City Navigator 7 under Virtual PC 7.0 with Windows XP Pro or 2000. I use a Garmin GPS V with a serial output which runs to a Keyspan USB-Serial converter. The Keypsan serial device is installed under Mac OS X, and in VPC preferences, I set the Keyspan USB-Serial device to COM port 1 or 2, and then it works fine in City Navigator 7. My Mac Mini is a 1.42Ghz G4 with 1GB of RAM. Unless I want waypoints really bad, I usually stick to roadnav or MacGPSPro though under Mac OS X. But yes it does work to use GPS input under VPC. The Garmin apps are coming to Mac OS X this year anyway though.
Did some more testing with powerbook and mapmonkey.
GPS works really well but occasionaly the audio (when giving direction) breaks up a little.
VPC sleeps and returns to where it was most of the time. However refuses to acknowledge the gps from time to time. The only 'fix' is to disconnect and reconnect gps. This can be a potential show stopper for me..unless I can find a fix/workaround !!