I've been using a PC laptop recently, which is a change from my desktop mac. One thing that's been a problem here is that I can't run photoshop on it and have had to run to my mac every time I wanted to do editing.
So I looked around and found a freeware, open source app called GIMP. It's pretty damned close to photoshop and it doesn't cost anything -- which is just my price.
Anyhoo, I've been screwing around with it to try to learn it and I made a few wallpapers for 1024X768 monitors. If your monitor's smaller, these will probably scale down. If it's bigger, then the last two are for you -- tile them and they'll work on any sized monitor.