I don't know if I can help so much on the UMPC front, but, looking at the specs (and price) of those things, they far out-do the puny little Nokia tablets. I feel that you would be sorely disappointed by the N810, as it doesn't have a universal OS, or any kind of horsepower compared to those. For a cheap, open source, basic use device I would recommend a Nokia internet tablet, but if you're going to be using fully blown XP applications, there's no way it can compete with the UMPCs out there.

Put short, I think that you're paying a bit too much for power you won't really use with the UMPCs. If you're considering a Nokia tablet, it's a cheap device, designed for handheld use (I hardly think Windows XP is designed for handheld use), with no frills. I think you'll have to have someone a bit more in the know than me to help you.