Hi David,
Welcome to the forum!
Since you've used and liked Microsoft Streets & Trips in North America, you could consider buying Microsoft AutoRoute with GPS receiver in Europe. You would get a software program you already know, and you would get a USB GPS receiver with it (just make sure you buy the bundle that includes the optional GPS "locator". I suspect some local computer stores or electronic stores carry it. If not, try Microsoft AutoRoute or see if you can locate a better deal somewhere closer to you.
If you just want a USB GPS unit alone (if you already have a GPS navigation software program), then look around for BU-353 (made by GlobalSat). It is a popular unit with a good reputation. It is based on the very good SiRFstarIII chipset. It costs around $50.
Not sure about the power supply. Hopefully others will suggest some solution.