I dont think its been posted here before ... but what the hell ... 
Make a custom message display prior to logging into your PC. While IT departments often use this technique to show legal warnings and network policies, you can customize it to say whatever you want.
1. Click Start, All Programs, Administrative Tools and Local Security Policy.
2. Expand Local Policies then Security options.
3. In the details pane double click Interactive logon: Message text for users attempting to log on.
4. Type in the message you want to appear.
*lifehacker.com/assets/resources/2007/07/Vista-Log-On.png
Source: Lifehacker have fun
Another Tweak
This registry tweak replaces the Delete command from the Recycle Bin with a Clear Temp command. This prevents users from accidentally deleting the Recycle Bin Icon from the Desktop. It also adds a Disk Cleanup command which performs an Extended Disc Cleanup on all disks. The Clear Temp command clears both Temp dirs: %UserProfile%\AppData\Local\Temp and %SystemRoot%\Temp.
*lifehacker.com/assets/resources/2007/06/Recycle-Bin.png
Download This
Also have a look Here
Make a custom message display prior to logging into your PC. While IT departments often use this technique to show legal warnings and network policies, you can customize it to say whatever you want.
1. Click Start, All Programs, Administrative Tools and Local Security Policy.
2. Expand Local Policies then Security options.
3. In the details pane double click Interactive logon: Message text for users attempting to log on.
4. Type in the message you want to appear.
*lifehacker.com/assets/resources/2007/07/Vista-Log-On.png
Source: Lifehacker
have funAnother Tweak
This registry tweak replaces the Delete command from the Recycle Bin with a Clear Temp command. This prevents users from accidentally deleting the Recycle Bin Icon from the Desktop. It also adds a Disk Cleanup command which performs an Extended Disc Cleanup on all disks. The Clear Temp command clears both Temp dirs: %UserProfile%\AppData\Local\Temp and %SystemRoot%\Temp.
*lifehacker.com/assets/resources/2007/06/Recycle-Bin.png
Download This
Also have a look Here
