Pam:
Here's what I did recently in my wife's office.
My wife is an architect, running AutoCAD 2007. AutoCAD 2007 won't work in any version of Windows newer than XP. The next release of AutoCAD after 2007 won't work in any version of Windows older than Vista.
Since she absolutely had to have something that worked, when I upgraded her PCs (from Windows 2000!) a couple of years ago, I chose to go with XP, because I had no doubt that it would work. In other words, there would be no fiddling and fumbling with anything; everything would work without any delay.
If I had had more time, then I would have gone with Windows 7 / XP Mode, and I would have tried to make it work. I probably would have succeeded, in which case she would have the latest (at that time the latest) OS and a new computer. But she is a small company and couldn't afford any downtime, so I went with the sure thing.
Since you are a VA and providing office services for other companies, I think that a great option for you would be to go with a Windows 7 computer for yourself, with XP Mode. Once you have it all set up and running successfully, not only will you gain the advantages of having XP on a new machine, but also you will know how to do that sort of thing, and you could provide that service for a customer, if they have some must-have software that won't run in Windows 7.
By the way, the "old / must-have" software scenario is the only case I can think of where I would do XP mode, because, as I mentioned earlier, there are some extra hassles that you have to deal with when using a virtual machine. But it could be a life saver in the case of old software.
You will have no problems running Office 2007 with Windows 2007. Or you could stay with Office 2003. There are lots of people using Office 2007, but I don't think there are very many using Office 2003. Again, if you go through the process of installing Office 2007 and getting it all set up and running, you will have gained some valuable expertise which you can then use for your customers.
Jim