Google turns up some interesting comparisons...
Interestingly, a lot of answers imply "Bamboo for personal, Intuos for professional".
Not having used a tablet myself, but interested, some time ago I looked around pretty seriously and asked questions here. I ended up deciding at the time that I wanted an Intuos 4. Never did get one (my budget was eaten up by other things). I see Wacom has come out with an Intuos 5 now.
My first tablet was an Intous 3, took some getting used to, now I cannot live without it. Also purchased a Bamboo to go with my laptop for portable use. The Bamboo is great, but for critical work I choose the Intous every time. They are not cheap and can last a lifetime if used correctly. Wacom has announced the Intous 5 and the prices for the Intous 4 are not too bad - they have them at a good price at Best Buy.
But warn your Art person that using a tablet is quite different than a mouse - but to get used to using it just have him/her play a few rounds of Solitair - that really helps with the eye/hand coordination.
Also there is a size difference between the Banboo and Intous - so check them out against available desk space.