The 'back /power button' combo is a great tip!
You can also do screenies using the SDK, using the DDMS application. I wrote about it here: www.hutsby.net/2009/11/howto-get-android-screen-shots.html
If its of interest I made a new wallpaper template which you can get here: sites.google.com/site/galaxytabwallpapers/
, and also some wallpapers which you are free to download and use for your own use - read about it here: www.hutsby.net/2010/12/galaxy-tab-wallpaper-template.html
Or just go straight there: www.fire-horse.co.uk/Galaxy_Tab_Wallpapers/index.html
. Just so you know, not all the wallpapers are 100% safe for work ;-)
PS Just like setting wallpapers on other Android devices, the built in tool does weird stuff, so you'll need the free App from the Marketplace called "Wallpaper Set & Save".
PS Loving the site!