How to extend Win7's trial to a full four months

If you install Windows 7 and don't enter an installation key, the 30-day activation clock starts. When the trail period is going to be expired, you can extend the free period another 30 days via the following steps:
Step 1: Click Start, All Programs, Accessories. Right-click Command Prompt and choose Run As Administrator. Enter your administrator password.

Step 2: Type the following command and press Enter:slmgr -rearmNote the space after slmgr and the hyphen in front of rearm.

Step 3: Restart Windows 7.Once the OS restarts, the Properties dialog described above will indicate that Windows 7's activation grace period has been reset to a full 30 days.You can run the -rearm trick a total of three times. If you perform a -rearm at the end of each 30-day period, you end up with 120 days of full, unfettered Windows 7 use without having to supply an activation key in the interim.