To achieve the perfect PC you’ll have to do some simple planning.
My advice is that you operate with at least 3 partitions; so if you only have one hard disk with one big partition, you’ll have to divide it into 3.
The drive letters for these partitions will typically be C:, D: and E:
Drive C - The Boot-driveOn drive C: You should strive only to have Windows. Windows likes to be alone!
It performs best when it rules the entire partition.
At the same time it needs some freedom, some free space; so you should size the C-drive so that Windows plus its virtual memory never takes up more than half of the drive-space.
For Windows XP a C-drive of 10 or 15 Gb will normally do the job.
On a Windows7 system it's more like 50 Gb.