I bought and downloaded a retail version of MS Office Home and Student for $89.99 along with a Korean language addition for $24.99 back in December. The OS I installed both into was XP. However, if I were to upgrade to Windows 7 Pro 64bit, then could I legally use the product key I got and use it, along with the Korean language pack?
Just to be sure, uninstall Office from the 'XP computer', then install the Win7 OS, and then re-install MS Office. I have done this per Microsoft's advice and did not run into any issues. This way you don't need to call Microsoft to activate the install.
I currently have MS Office Home and Student (3-user) and plan to purchase Office 2010 during the Thanksgiving sale, and at that time I will transfer the older Office 2007 to older desktops in our household.