Purchase of a product key card for Microsoft Office 2010 saved me a substantial amount of money, given that I needed only one license. (The CDROM product provides licenses for installation on two computers, e.g., a purchaser's desktop and laptop.)
Office 2010 was not preloaded on my target computer, so I downloaded the software from the web site named in the key card instructions. To get the download, you must enter the product key, which is case sensitive. (You must use caps for the letters in the key.) The web site gives you the option of purchasing a backup CDROM if you're a nervous nellie like me. The web site also gives clear instructions on how to proceed after the download.
The software download (585MB) took about two hours with a relatively slow DSL connection. Installing the software requires the product key to be entered for a second time (include the hyphens). The installation itself took about 15 minutes on a 1.67 GHz netbook, which had a trial version of Microsoft Office 2007 installed that needed to be removed. (The installation screen gave the option of removing a previous Office installation or leaving all or parts of a previous installation on the computer.)
As often happens with Microsoft products, the "installation progress bar" finished a few minutes before the installation itself was finished. The product then required a reboot to finalize the installation. For me, the only really anxious moments involved in the entire operation were the moments spent waiting and watching the screen while the computer was verifying the legitimacy of the product key.