The following describes the Registry key that's involved.
Step 1. While running a copy of Windows Vista that hasn't yet been activated, click the Start button, type regedit into the Search box, then press Enter to launch the Registry Editor.
Step 2. Explore down to the following Registry key:
HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Windows NT \ CurrentVersion \ SL
Step 3. Right-click the Registry key named SkipRearm and click Edit. The default is a Dword (a double word or 4 bytes) with a hex value of 00000000. Change this value to any positive integer, such as 00000001, save the change, and close the Registry Editor.
Step 4. Start a command prompt with administrative rights. The fastest way to do this is to click the Start button, enter cmd in the Search box, then press Ctrl+Shift+Enter. If you're asked for a network username and password, provide the ones that log you into your domain. You may be asked to approve a User Account Control prompt and to provide an administrator password.
Step 5. Type one of the following two commands and press Enter:
slmgr -rearm
or
rundll32 slc.dll,SLReArmWindows
Either command uses Vista's built-in Software Licensing Manager (SLMGR) to push the activation deadline out to 30 days after the command is run. Changing SkipRearm from 0 to 1 allows SLMGR to do this an indefinite number of times. Running either command initializes the value of SkipRearm back to 0.
Step 6. Reboot the PC to make the postponement take effect. (After you log in, if you like, you can open a command prompt and run the command slmgr -xpr to see Vista's new expiration date and time. I explained the slmgr command and its parameters in my Feb. 15 article.)
Step 7. To extend the activation deadline of Vista indefinitely, repeat steps 1 through 6 as necessary.
Any crooked PC seller with even the slightest technical skill could easily install a command file that would carry out steps 1 through 6 automatically. The program could run slmgr -rearm three times, 30 days apart, to postpone Vista's activation deadline to 120 days. It could then run skip -rearm every 30 days, for a period of months if not years, by first resetting the SkipRearm key.
The program could be scheduled to check Vista's activation deadline during every reboot, and to remind the user to reboot once a month if a deadline was nearing. The buyer of such a PC would never even see an activation reminder, much less be required to go through the activation process.
If you happen to buy a Vista PC from a little-known seller, and the price was too good to be true, use Vista's search function to look for the string SkipRearm in files. You may discover that your "bargain" computer will mysteriously start demanding activation in a year or two — but your product key won't be valid.
I asked Microsoft why SkipRearm is included in Vista if it can be used to create machines that appear not to need activation for long periods. A Microsoft spokewoman replied, "I connected with my colleagues and learned, unfortunately, we do not have information to share at this time." (I can't identify the speaker because the policy of Waggener Edstrom, Microsoft's public-relations firm, prohibits the naming of p.r. spokespersons.)
In my testing of Microsoft's back-door loophole, I've found that the technique can be used to postpone the activation deadline one year or longer. It may or may not, however, work forever, as I describe below.
paano toh pg tapos ng 90days?.. maganda sana kung ma activate talaga para no worries.. 
