There are three key ways to get more space on your C drive
1) As ksiemb suggests, clean up the c**p on your C drive. It would be useful if you told us how big the C drive is, how much is used, and whether it is the whole drive or a partition.
There are many things that can be removed: Reduce the size used for restore points, purge your temp files, remove the uninstall files that get crammed into the Windoze directory by every update / SP.
2) Buy another drive for data and move big things like your music library there. My Documents can actually be modified to point to a directory on the new drive.
3) Buy a bigger drive and clone the old one to it. Boot from the new one. Presto, more space.