Dont be a 'er in help threads
For your problem... Go to the alteriwnet site and click on the topic "new updater, (click me now, pronto etc.)
Download the new updater and paste it into your cod mw2 directory for aIW (copy and replace the files, optional)
Now be sure that you run iw4mp.exe AS ADMINISTRATOR (Right click -> Run as Administrator) NOTE: you need an administrator account on your PC to do this!
Now let it update, if its stuck, restart it AS ADMINISTRATOR and keep restarting if its still stuck untill its finally done updating.