Hi purple people eater.
Further to the suggestions above, I would recommend SEQUOIA VIEW available HERE
. It will give you a graphic view of every programme on your HDDs by size and it is easy to see what is bloating your system. Mousing over each will tell you exactly where it is located. An excellent programme and fun to use.
The pagefile takes overload from your RAM to your HDD and it is usually recommended that the size be set at least 1.5 times your physical RAM. If you can set up your pagefile on a separate HDD this works better as you then have two heads doing the work of reading and writing.
Buddy215 makes a good point about whether you are concerned about 'memory' or 'free disk space'. I imagine you are talking about both.
xtatik222k also has a good point re 'system restore points'. These can take up a lot of space, which is usually fixed for this purpose, but they can also contain infected files if your system is infected when the restore point is made, so it is not a silly idea to clean them out occasionally. When you are happy that your machine is running smoothly, you can make a new restore point then go to START/All Programmes/Accessories/System Tools/Disk Cleanup- more options - system restore cleanup, which will delete all but the most recent.
Good luck. Cheers