Prevent drive letters from changing when installing windows

I intend to reinstall windows 7 on my pc because of a windows disc I bought being counterfeit and any time I have reinstalled windows xp when I had it, all my drives/partitions letters were all changed. I always took the bull by the horns and relettered them again as they were, hoping the data on the drives would still be okay. Up to now they have been. I read an article when researching windows 7 that told how to prevent drive letters from changing during install, but I read that much, I can't even remember where I read it. As I have 24 drive partitions on my pc, you can understand why I don't want the letters to change, if possible. I would be grateful if anyone knows how to do this, or can point me in the right direction. Thanks for reading and in advance for any help offered. hedley

24 drive partitions on my pc

Just out of curiosity, 24 partitions?

That should have been 14, but in counting when I relettered them there are actually 16, not counting the C: drive: 40 gb C:\ drive for windows only 120 gb drive partitioned in three 80 gb drive as one drive 500 gb drive partitioned in 4 2 x 1tb drives each partitioned in four Thanks hedley