Reinstalled Vista

I reinstalled Vista so that I could have a clean copy, minus any Dell bloatware, and I just have a few questions.

First, I have a Dell XPS 630i, with 32 bit Windows Vista Home Premium, and when I reinstalled Vista I noticed that I'm now using around 100 gigs of storage on my Hard Drive C (I have 350 gigs free of a total 450), whereas before I did the reinstall I was using a lot less storage space than that.  What gives?  When I did the Vista reinstall, it said that there would be a copy of Windows Old made that would take up space, but I used Disk cleanup and got rid of those files.  What else can I do to get rid of stuff on my hard drive?  Btw, I have very few programs installed on my hard drive now that I've done the reinstall, and when I go into My Computer and try to count up the space I've used (looking at program files, music files, documents, etc) I only count up about 30-40 gigs that I've used. Where did that other 60-70 gigs go?

Second, I think I have all my drivers updated now, but I wanted to check about the driver for my graphics card.  I have an Nvidia 9800 GT 512 mb card, and the driver that was included on my Dell disk was dated 5/5/2008.  However, I found a driver on the Nvidia site (this is the driver here:  http://www.nvidia.com/object/winvista_x86_177.79.html) that is dated 7/29/2008, but when I update my driver in Device Manager it rolls me back to the older driver.  I suppose it's because the older driver is digitally signed, but the newer one isn't.  My question is, does it matter that the newer driver isn't digitally signed, especially since I got it directly from Nvidia?  I'm kind of a newb when it comes to this stuff, so that's why I ask.  ;)

Finally, after doing the reinstall of Vista, I just want to make sure that I've done everything correctly.  Is there anything major you're supposed to do after a reinstall?  Everything is working great and seems to be running smoothly (apart from the fact that a lot of my hard disk space seems to be being used for some reason), but I just wanted to make sure.

Thanks!