I own a Samsung Q1 Ultra (note Ultra, that's the one with the two keyboard halves to each side of the display). I have the Windows XP Pro version, with 1GB RAM and 60GB hard disk. Not sure how much horse power you'd lose on the Vista versions. I loved mine from the minute I discovered it, when I finally bought it, and ever since. It's a brilliant part.
I have ArtRage 2.5 UMPC (in addition to ArtRage 2.5 for Windows, which I use on a fairly powerful XP machine). I use both devices frequently, and use the UMPC version more and more in the evenings, for sofa-based sketching, replacing sketchbook and pencils.
In terms of drawing performance, I don't find much difference between the two. Complex operations such as hiding or enabling layers might take slightly longer on the small UMPC. I am sure if you compared ArtRage on both devices with a stopwatch, more differences could be noted, but from a user experience standpoint of view, I find it works just great.
One key difference is that the Samsung's tablet is not pressure sensitive. You get used to changing the pressure with the cursor keys (under your left thumb). Since members on this forum advised me on the advantages of a true, pressure-sensitive, graphics tablet, I bought a Wacom Bamboo Fun for the desktop PC. I love it, but find that I am so used to not controling pressure through the pen that I still often use the cursor keys for pressure-adjustment, even on the desktop.
In short, the Samsung Q1 Ultra is perfectly adequate for ArtRage 2.5 in my opinion.
It's not about how many breaths you take; it's about the moments that take your breath away.