With iOS UserLand JB out and all thanks to COMEX & Dev Team, you can now manually modify plist file to enable MultiTasking & WallPaper on iPod Touch 2G & iPhone 3G.
Links for JB are below
ModMyI Mirror Link
Now all you need is iPhoneBrowser and go to the following directory
Save the N72AP.plist on your computer. Download PList File Editor free from iPodRobot website
PList File Editor
Install PList File Editor and open the N72AP.plist file and add the following key/value pairs
For Multitasking Add the following
For Wallpaper Add the following
Save the changes to the .plist file and upload it on the iPod Touch or iPhone via iPhoneBrowser in the same directory i.e. "/System/Library/CoreService/SpringBoard.app/"
Restart iPhone/iPod Touch and you will have both feature.
To Check the WallPaper navigate to Settings > Wallpaper and you will get an option of setting the wallpaper for homescreen & lock screen
To Check Multi Tasking, double press the HOME Button and it will show all the apps which are currently in background. You can click each app (press & hold HOME) and it will let you kill that app. By default and app that is closed goes into background.