I recently purchased a GPS (Garmin 2610) to tote around on motorcycle trips. If you have never tinkered with one - it is VERY cool. Unfortunately the MapSource software that comes with it requires Windows... Ugh.
I've run VMWare and QEMU on my Ubuntu box before. VMWare was very nice but a pain to install (granted it's been awhile so that may have improved). QEMU was very fast but recently it's been a bit flaky and this time when I tried to run Windows it wouldn't find my USB mouse. I dug around online but was unable to fix it. I've heard about VirtualBox for awhile now and decided to give it a try.
While VirtualBox is free - I did notice they were recently acquired by Sun and now it appears they have two versions: one closed and one open-source. So far I'm very impressed. I ran into some issues installing the OSE version from the Ubuntu repositories. Downloading the .deb file from the VirtualBox site worked much better. Installation went well and I installed Windows XP without a hitch. And most importantly everything works - mouse, keyboard, internet, etc.
So if you are looking for a VM - check it out - they have an extensive list of supported platforms and Linux, Windows and Mac are all supported in one flavor or another. Lifehacker did a recent article covering installation and running Windows apps seamlessly on the Ubuntu desktop.