OT: PC Cleanup

[AgentZero]

I swear, one of these days I'll post on-topic. Really! Anyway, I'm just doing a bit of maintenance on my computer to keep it running nicely until I get employed & am able to dump my money into a new one. At the moment, I've got Windows on a seperate partition, but that partition's starting to get a little clogged. I've identifed the two main culprits: Program Files and Application Data in the Documents and Settings folders, the latter being the worse of the two. And I'm just wondering, is there anything really important in Application Data, or could I just nuke the whole thing to free up some space?

Also, does anyone know if there's a way to have the Windows program itself on one drive, but have Documents & Settings and Program files on a different drive?

Edit: And what exactly does Pagefile.sys do? I was under the impression that it's the Windows swap file, but I've just noticed I've got one one each partition. What's going on there?