The best thing to do in my opinion is to buy an external hard drive for all your documents, music, pictures etc. If you have Windows 7 you can tell your pc that the external hardrive is your library, that way the shortcuts in Windows Explorer still work. That way you can use your internal hard drive for only programs. This is beneficial for a couple of reasons. Firstly, you free up space for programs. Secondly your pc will run a bit smoother as word docs, pictures, etc take up lots of single sectors increasing your disk fragmentation. Programs, on the other hand, will occupy large chunks of sectors. Obviously running defrag is always useful.
Buying an external hard drive is quite cheap these days. Alternatively you can always buy a new internal hard drive. Again, they're not that expensive.