code:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\RecycleBinOnDesktop]
"RegPath"="Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\HideDesktopIcons\\NewStartPanel"
"Text"="Show Recycle Bin icon on the desktop"
"Type"="checkbox"
"ValueName"="{645FF040-5081-101B-9F08-00AA002F954E}"
"CheckedValue"=dword:00000000
"UncheckedValue"=dword:00000001
"DefaultValue"=dword:00000001
"HKeyRoot"=dword:80000001
That'll work much nicer than matty's, it adds a nice little option into Folder Options meaning you can just toggle it on and off when needed, instead of re-applying two different reg files.
Add the above code to a text file and rename it <name>.reg. After saving it double click it to import to registry.