Make your plan first. You should keep about 10GB for your Windows and most commonly used programs (C-drive). Use a 20GB partition for games, big programs like Office or photoshop etc. Uninstall these games/programs first and then re-install them in the new partition. Make a partition of about 30GB for music, and make the fourth and last partition to use up the rest of the space for personal data (like My Documents) and backups.
Actions in Partition Magic, in this sequence:
resize current 80GB down to 10GB or as small as will fit.
make a partition of 15GB at the very end of the HD (backup and personal data)
Make a partition of 30 GB just before that (for music)
Use up the rest (between first (windows) and third (music)) for programs and games. This will be about 20-22GB.
Format all new partitions in NTFS
Boot into Windows when done. Use Explorer to shift stuff around (drag and drop).
You may have to resize C: again after all the shifting (down to 10GB), and make the next one (games etc.) larger to use the leftover space.
If you can, make backups of all your important data before you start with PM. This program has been known to mess up horribly.