i just stumbled upon this hack.
1. Click on “Start button -> All Programs -> Accessories“. Right-click on “Command Prompt” and select “Run As Administrator“. If you are prompted to enter password, enter the password and continue. You can also open Command Prompt in Administrator mode by typing “cmd” in Startmenu Search box and press “Ctrl+Shift+Enter“.
2. Now provide following command:
3. You'll be prompted to restart Windows, restart it and the trial period will be reset to 30 days again.
4. You can use the same command 3 times. In this way you'll be able to use Windows for 120 days without activation.
5. Now its time for the main trick. Open regedit and goto:
6. In right-side pane, change value of SkipRearm to 1.
7. Now you'll be able to use the slmgr -rearm command 8 more times. So you'll get total 360 days for using Vista and 7 without activation:
120 days by using slmgr -rearm command before registry editing
240 days after registry editing
EDIT: cant post the link to the original website for some reason. ill get back to you with that.