XP Pro on the laptop, in the past it has had Win2k, Mandrake 10, and most recently Ubuntu 5.04
I've really tried to get into Linux, but a few things hold me back:
1. the learning curve is fairly steep, and taking a lot of time to learn an OS doesn't fit all too well into my schedule
2. openoffice is no Office, and Office is the standard amongst my fields of study
3. the wireless networking support in Linux leaves a lot to be desired (in specific, built in or at least easy to install and use wireless network roaming/switching - Windows whips Linux on this front)
So, it's XP for the time being (which in all honesty works fine and is very stable on this laptop), with the occasional dabble in whatever the new hotness is for Linux distros.