There are tools like partition magic (and others - http://en.wikipedia.org/wiki/List_of_disk_partitioning_software ) which should do the job.
> and D about 20 gb. Due to (my music) collection growing now to 80 gb
Even if you absorb the whole of D into C, you're only extending your collection space by 25%. How long will that last?
If you've got all the original install disks (and downloaded all the latest drivers for your machine and burnt them to CD), then spend the money you might spend on a s/w licence you're only going to use once or twice, on the biggest HD you can afford (you'll probably double the space on what you have now).
Plus your system will benefit from being a nice clean install with no accumulated crud.
Plus your old disk is handy for backups, or experiments with other operating systems, or just generally as a big data disk for all your collection.