Interesting.
I wonder if the block allocation size changes when you partition the drives... (your OS might have formatted your partitions so that the file pieces are much smaller. Smaller chunks may help you out in performance)
If you are seeing slow install on one OS, and faster install on another OS, it is possible your IDE or CD-ROM drivers are 'better' for a specific OS. (i.e., the data is read from the CD faster..)
Otherwise, I don't really have a clue why it would have installed faster
- rp