Last January, I featured VirtualBox, another open source virtualization software, along with a link to a Tutorial on how to install it on Edgy Eft.
Here's another tutorial on how to install VirtualBox but this time on Ubuntu Dapper Drake (6.06) as host and Debian Etch as guest OS. Check it out, it has plenty of screenshots.
So why use multiple computers, when you can run multiple computers virtually, right? At least this is what I do – running other operating systems on top of my Macbook Pro.