iMac suddenly slow when booting to Windows 7

I have an iMac with a 250 GB HDD, partitioned with 200 GB for OSX, and 119 GB for Windows 7 Ultimate, 32-bit. I have 85 GB left on the mac side, but only 11 GB left on the Windows side. I have 4 GB of RAM, but since I didn't really understand the difference between 32-bit and 64-bit software when I put Windows on it, Windows can only use 3 GB of memory. My issue is that a few weeks ago, I shutdown on the Mac side to go to Windows, and when I booted up in Windows, I knew something was wrong. It took a long time to boot up, everything from the "Starting Windows" logo to the "Welcome" after I logged in. After that screen went away, the screen was suddenly black, except I could see and move my mouse on the screen. My desktop eventually loaded, but even simple things like opening the Start menu or a folder took a long long time. Lots of things weren't responding, so I gave up and shut it down. At that point, I had about 4 GB of space left on the Windows side of the hard drive. A few days ago, I bought an 750 GB OWC Mercury Elite Pro external HDD, and backed up my Windows side. I then deleted the temporary folder on Windows, and some large files I didn't need anymore. This got it to 11 GB left. I also have my Mac backed up with Time Machine to a 250 GB external drive. My question is, what is making Windows so slow? Is this a sign that my hard drive is suddenly going to fail? The Mac side is running better than ever, actually, which I think is with the help of the 4 GB of RAM that I put in about 4-5 months ago. I have tried defragmenting my drive and running Disk Cleanup. These both haven't helped much. I don't really want to delete any of the files because I really need them all, especially if my backup drive fails. If anyone could help me out that would be great because I have had this problem for a while now, and I would like to be able to use Windows again!