We used this laptop-tablet this year:
http://www.amazon.com/Lenovo-ThinkPa.../dp/B000RBB8YO
Our mentor just received his Alienware laptop, and decided to give us his 4 year old Thinkpad X61 tablet. Ours had a Core 2 Duo processor, 500GB, 2GB RAM and a special SSD memory device to boost top speeds. Needless to say it worked perfectly. Booting up took less than 20 seconds, and we could go from shutdown to field-ready in under a minute.
The only cons was that there was no DVD drive, you would have to buy the expansion base separately, and the screen was a little hard to see outdoors. Oh, and you could only input using the screen/stylus (which were surprisingly accurate), or the red trackpad thingy - there was no touchpad.
If you want to do a fresh install, all the current drivers (most updated in 2012) are easily available on Lenovo's site. Just make sure to install Wacom's special driver as well. Ebay prices are $400 - $700 depending on condition.