Depends what your MBP has to say about it.
When you get the pro, and start doing what you'll be doing with it, open up activity monitor. If it states you have no free ram left out of the 2 gigs, or shows that you have page outs, I'd then start with the ram.
Oh, and if you'll be using parallels, you may as well get 4 gigs. It just LOVES the ram...
As for earlier comments about 7200 hard drives, check out some reviews at tom'shardware.com. The new 7200's didn't use that much more energy than many of the 5400's.