Registry Hacking

Display legal notice on startup:

Wanna tell your friends about the do's and dont's in your computer when they login in your absence. Well you can do it pretty easily by displaying a legal notice at system start up.
REGEDIT
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system]
"legalnoticecaption"="enter your notice caption"
"legalnoticetext"="enter your legal notice text"

Automatic Administrator Login:

Well here's the trick which you can use to prove that Windows XP is not at all secure as multi-user operating system. Hacking the system registry from any account having access to system registry puts you in to the administrator account.
REGEDIT 4
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
"AutoAdminLogon"="1"

No Shutdown:

Wanna play with your friends by removing the shutdown option from start menu in their computer.
Just hack it down !!!
Regedit
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer
"NoClose"="DWORD:1"

Menu Delays:

Another minor and easy tweak to remove any delay from menus sliding out. For this you will need to use regedit (open regedit by going to Start -> Run..., then typing 'regedit' and pressing enter). The key you need to change is located in HKEY_CURRENT_USERControl PanelDesktop. The actual key is called MenuShowDelay - all you have to do is change the value to 0. Remember, you will have to re-boot your computer for this tweak to take effect