Installing PlanetCCRMA on your PC is not quite a labor of love, but it does take some attention. Most are coming to this process with a Window's Installation currently on their PC, so we'll take that assumption here. Questions?
Backup Your Data
You must have a backup of your data! What kind? The answer to this question will do it... "To what extent should I backup my data such that if I lose my current partition and my data is lost, will I not have an emotional reaction?" This answer to this question and what you choose to do about it is entirely your responsibility.
Here are some helpful links for Windows users:
Establish a Disk Partition
You will also need ~10Gb of unpartitioned free space. If you have only a single Windows partition on your PC, this may mean that you will need to resize this partition to make this free space. You can do this in one of two ways:
free: gparted LiveCD
not free: Partition Magic