Before you send me an e-mail, please check this FAQ - you might find the answer.

 
1. How does Hook99 work? Does it tweak the register or what?

Hook99 is not a registry trick. It changes caption and bitmap on-the-fly.

 
2. Could you tell me where the registry entries for the start button are located?

AFAIK, such entries don't exist.

 
3. Is there any way to make the changes in the start button permanent, without starting the program everytime I start windows?

No. Create a shortcut to Hook99 in your StartUp folder.

 
4. Can I see your source code?

No.

 
5. Is there any way to disable DeskTask's screensaver icon?

Open desktask.ini and change line:
TrayScrn=1
to
TrayScrn=0
You can access settings menu with CTRL + right click.

 
6. I would like to change Desktask's tray icons.

Use IconTask and IconScrn settings in the desktask.ini:
IconTask=C:\windows\system\shell32.dll,34
IconScrn=C:\anyfolder\anyicon.ico