Most of the tests I've seen show only marginal differences in most usage between the 7200 rpm and 5400 rpm models, but obviously there's an edge to using the 7200 ones. The 4200 rpm drive will be noticeably slower.
Personally, as a developer and one who is very dependent upon disk speed, I'd go with the 7200 rpm and spend the extra money on an external with additional capacity. That said, the laptop work bought me has a 5400 rpm drive, and it seems adequate. I'd shy away from the 200GB model unless you have more need for storage than speed - but note that it's fine for most use, just not really for apps that pound on the disk.
You're going to start with ~20GB occupied with the OS and all of the pre-installed apps. 100 "GB" drive => ~93GB of real space (due to that whole 1000*1000*1000 disk manufacturer "gigabyte" vs 1024*1024*1024 gigabyte the computer uses). 160 "GB" =>~150 GB. Make sure you at least get a drive big enough, because a fast drive without all your stuff is relatively useless.
Battery usage probably is roughly the same, all things considered, for all of the drives.
