Rule #1: Don't install anything unless you're 100% sure what it does.
Rule #2: See rule #1.

Re separate partitions, they aren't as strange an idea as you might think. If you need to reinstall Windows, it's usually best to completely clean down whatever it's living on, to make sure there's no stray crap left hanging around (eg. programs still in C:\Program Files but without registry entries). If all your data is on a separate partition, you can format the C: partition and still have your data intact on the D: partition.

Thankfully Windows doesn't die as often as it used to, but it's still a trick worth knowing.

Graham.