I don't know about the CPU upgrade, but RAM can go up to 2.25GB, despite what the specs say!

Lots of people over at ASUS forums have done that, including myself! This is more than enough for Win XP Tablet (from my own experience) and also Win 7 32bit (from what I've read by other users). Also, removing ASUS bloatware, and using nLite to strip down XP results in a zippy-enough system even with the stock processor.
I doubt there are any more “new” R2H’s out there. Google has a couple of stores saying they have it in stock (not sure if it’s new or refurbished) and sell it for $1100-1800. I am also selling mine at eBay right now; give it a look if you want to.
http://cgi.ebay.com/ASUS-R2H-UMPC-XP-TABLET-FULL-EXTRA-LIKE-NEW-/140468441481?pt=US_Tablets&hash=item20b4925189
Take care