Just a couple of quick ones... I was going to run straight through the installer but it did indeed look like it was going to eat windows. Not knowing how your Ubuntu is actualy installed could be a wild card. If it were me I would fire up backtrack via usb or dvd and run the gui partitioner to look at the drive.
Another thing. Your current dual boot setup, what boot loader does it use? Grub? Lilo? Whatever you have if you play with the partitions and systems you are going to have to edit it to point in the right directions to be able to boot into any of the installed systems.
I used http://forums.remote-exploit.org/bac...dual-boot.html
Remember you are going to have to use different partitions than that so you can still get to windows. Also if you do indeed only have one partition you are going to have to unmount it and resize it.