low hand answer

I remember that IDE/ATA drive can hold up to 4 primary partitions. But if you set up an extended partition then you can further partition it up to 23 logical partitions(drive letter from D to Z). However some OS must reside on the primary partition and some dose not have to.
Just like the other guy said, it is too fancy for you to install so many OSs. Anyway as long as you can learn something from it, it is worth of a try.
By the way, what are those 7 OSs. You must have bought it from SS! Just kidding!
Good luck!

--文學城www.wenxuecity.com--