Couple of things that could help you out a bit, hopefully. Harddrive clutter needs to go and the biggest culprit of creating it is the Recycle Bin. By default, everything you delete or uninstall is put in the Recycle Bin. Not a problem, right? Wrong! The recycle bin creates a hidden folder, the first time you empty it and it keeps putting everything in that folder, when you empty it. Change your settings on it by right clicking on the Recycle Bin, left click on properties, then click the radio button where it says "Don't move files to the Recycle Bin. Remove files immediately when deleted.", then click Apply, OK. Then empty the Recycle Bin. This deletes everything in the hidden folder and the folder, itself, freeing up a huge amount of drive space. Defrag your hard drive(s). I use AusLogic's Disk Defrag utility, instead of trusting windows to do it properly, for 2 reasons, AusLogic's utility is way faster than windows and will optimize your files, while it defrags the drive.
If you're using a 32 bit version of windows, you're limited to 4 Gb of ram and if that's what you have, you're stuck with it, even if the motherboard will handle up to 16 Gb or more. Going to a 64 bit version of windows will allow you to add more memory, to your PC, without having to rebuild it, from the ground up. Also, if you're not all thumbs and don't mind waiting, you can buy a new PC, one part at a time, from Newegg.com. Get a new motherboard, this month, new CPU next month, etc., assembling it all, when you've got all the parts you need/want.
Getting back to the hard drive problem, that's caused by a hidden file (pagefile.sys or swapfile.sys, I think) that needs a lot of drive space, on 32 bit systems, to work as intended. This is usually a fixed amount of hard drive space, allocated during installation of windows and does change in size, depending on what else is hogging your HD space. In your case, I think it's your recycle bin folder, which uses up more and more space, each time you uninstall or delete something. Adding more memory will reduce the load on the pagefile.sys section of your HD and reduce HD usage. Again, though, adding memory is dependent on two things. Are you using a 32 bit version of windows and what is the maximum amount of memory your motherboard can handle.