You have to have a previous verion in order to install the upgradable version of 2007. I wish it weren't the case, as it would make building new clients much easier for me.
 
From the way you worded the question, it sounds like the version of Office is already installed on your system. Are you saying that your machine came with a validated version on it originally but it currently is not installed on it?

Thanks for responding. I am saying there are fully validated versions of Office 97, 2000 and 2003 on all the computers in question but I don't have the actual original install discs. This is for my wife's small business (not the owner, but she is the COO). All her installs are legal but the Office Manager who was in charge of the software upkeep recently left the company and no one knows where the discs are. They want to update to 2007 and I need to know if I can just order the upgrade versions or if I have to order full versions. Thanks for the help.

Anybody?

Unfortunately in MS opinion if you don't have the install discs then your copy is not strictly legal. Hence the reason they put the key on the disc case with a message to store in a safe place.
 
You might have to harass the former Office manager to disclose the location of the discs if you need to reinstall the older Office software!
 
However if Office is already installed on the computer you should be able to use the upgrade path. Office2007 will ask when you install if you want to keep or upgrade the existing office installation. Upgrade overwrites the existing installation.