I guess this is old news (especially if you read Slashdot) but VMWare has released a runtime version of their VM software calld VMware Player as a free download. I have always been a fan of Virtual Machines and other emulators. QEMU has been my favourite so far with it's kqemu accelerator module. I frequently use it to test different Linux distros and Live CDs. I've also got Windows 2000 and Windows XP running under qemu at tolerable speeds. However VMware Player performance is quite amazing.
Another thing that makes VMware Player so interesting is that it runs very reliably on Microsoft Windows. If you are a reluctant Windows user (because of restrictions at work) or a Windows user wanting to try out Linux, get the VMware Player and download the Browser Applicance Virtual Machine. "Browser Appliance" is a working Ubuntu Linux image. Though it's an older version, it's a full fledged working installation, so you can install additional packages or even upgrade over the network. The VMware configuration file is a simple text file and can be tweaked to install your own OS if you desire but "Browser Appliance" is a great way to play with VMware Player before you try more advance things.