i see this topic has split into two threads...clean install and backup/partitions. as for the original question, you can install one on top of the other but in my experience it is better and less of a headache to do a clean install. as for backup/partitions, i am a big fan of multiple drives. until this past upgrade, i had a 30gig drive and a 40gig drive. the 40gig drive was for storage, including divx movies, mp3's, videos, and any important date that doesn't actually get "installed" (meaning it's stuff that doesn't need to mix with the operating system to run or be opened). the 30gig drive was for windows, program files, basically anything that gets installed and mixes with the operating system. this obviously left plenty of room...which comes in handy for temporary space (hey, *.VOB files take up gigs of room until you're done with them). also, all the not-so-big stuff that was on the storage drive but was really important i would zip up and keep a copy on the main drive, just in case. now, since i have filled up the 40gig drive and i'm saving $$ to get another ~60gig drive, i have my main 30gig drive partitioned as 10/20, with the same principle as before but using the 20gig partition as an overflow from the 40gig drive. ok...no time to proof-read, did that make sense?