How can I buy a product key for Microsoft Office 2007?

I bought a new Acer laptop about 1 and half months ago that came with Vista and Office 2007 TRAIL preinstalled. Now as the trail is about to expire I want to buy a Office Professional 2007. But that will put some extra work for me like uninstalling and reinstalling etc. Hence I was thing if there is any way I can buy license key from Microsoft and convert this trail in full version. I tried searching for the same but dint found the place where I can but the license. Any suggestion please?

Yes, you can buy a "Full Version" license. Check out these Microsoft knowledge base articles for the process and other informations:

How to convert a trial version of a 2007 Office suite or program to a full retail perpetual license version:
http://support.microsoft.com/kb/927756/en-us

How to buy the 2007 Microsoft Office suites:
http://office.microsoft.com/en-us/su...px?ofcresset=1