Keep in mind that the entire MacBook family – the MacBook and the MacBook Pro – all use Core Duo 2 processors, and there isn’t a huge difference in speed between them. You’re primarily paying for screen size and video cards.
From what I’ve read, AutoCAD will run well on any MacBook in Boot Camp, provided you max out the RAM. Remember that Boot Camp is not an emulator – running AutoCAD in Windows on a MacBook is exactly like running AutoCAD in Windows in a similarly-specced PC, so basically if you’re currently running AutoCAD on a P4, it should feel faster on a MacBook.
If you’re going to be doing lots of 3D work, you might want to consider a MacBook Pro, because the regular MacBook has an integrated graphics card. However, everything I’ve read has indicated that the regular MacBook should be more than sufficient for “student work”.
I’ve never actually used AutoCAD, so take everything I say with a grain of salt – I’m going off of others’ experiences.
[edit]: Oops, didn’t see your last post. If price isn’t a huge factor, then definitely go for a MacBook Pro. 👍