I don't know how to free up space to install Windows Vista on Unbuntu 8:10. It says at least 392 MB for installation. I'm desperate to play the Sims 2 game again but haven't been able to since using open source. I've installed wine but the game does not play and crashes as it is not supported. It was a treacherous task that took a few hours as to learning how to use "wine eject" in the terminal to eject the disk for installation. So, since Vista was previously on the computer I am using, I plan to dual boost but can't because I don't know who to free up MB or GB.
Use Gparted (free download) to create a partition for Vista, give it at least 10GB.
Make sure you backup all your data before proceding, there is always a risk of loosing data when using such tools.