You must use XPostFacto to boot from the 10.1 CD. The installer checks whether you have 10.0 installed, if you do you can choose to update or perform a fresh install (which is much quicker). It's possible to make a copy of the 10.1 CD that allows installing without an existing 10.0 installation, you have to create an image of the CD and then delete a certain file (I don`t remember the exact location and name, it was something like "checkforx", I found the info about it somewhere on the net). And while you're at it, you might also use XPostFacto to modify the image so you can boot from the burned CD without using XPostFacto.