Enthusiast is right; there is no cheap or easy way to re-partition or move apps.
Do you keep a lot of data files in your My Documents folder? If it is the case that the amount of space used by My Documents alone is a majority of the reason you are out of space on C: then you may wish to move the location of your My Documents folder to D: like so: http://support.microsoft.com/default.aspx?...B;EN-US;q310147
If your principal data dump is somewhere other than My Documents but it is on C: then just move it to D:
If it's less a data issue and more an applications one then I suggest this. If you are running out of space on C: but have plenty on D: AND you have the installation discs or files for some of your applications that are installed to C: I would recommend uninstalling them from C: and reinstalling them to D:. And in the future install any apps to D:.
Hope some of that helps. Everything Enthusiast says stands by the way. These are just some cheap DIY solutions you may wish to consider.