A new version of the Ubuntu OS, dubbed "Hardy Heron" is coming out soon. To celebrate its release, I've added a countdown image on the right hand side. Clicking it will take you to the Ubuntu homepage.
You can test Ubuntu on any machine (32 and 64 bit versions are available for Intel, AMD and Sun Sparc machines), or virtual machine. It has very low hardware requirements. You can also "try-before-you-buy" by using the LiveCD option (it allows you to boot the system and play with it, without installing). And did I mention it's free?
Read my review of the current version of Ubuntu here.