You would only do that in an insane asylum. However, to downgrade from 7 to Vista (if you decide to make that incredibly dumb move) you will need to create a seperate partition for windows 7 with the disk manager tool, I forgot what the directory was, but it's something like diskmgmt.msc. Create a partition about 30GB (or larger if you need to backup stuff) in size at first, restart computer with Vista CD in, wait for it to load all its stuff, then choose the partition with nothing on it to install. Once you get into Vista, you can use the diskmgmt tool to delete or possibly combine both the windows 7 and Vista partitions. If you delete the 7 partition, choose the Vista one and just click "Expand" so you can use that HDD space. Or you could have the two partitions seperate and have yourself a dual boot system.
