That seems a lot of trouble to go to just to use MS Office when OpenOffice.org
is free and will do almost everything MS Office will PLUS it can make pdf files
with a mouse click.

When you start VirtualBox, you should see a window on the right side with 3 tabs
marked "Details", "Snapshots", and "Descriptions". Right click "Current State"
and select "Take Snapshot", OR with Windows running click on "Machine->Take
Snapshot" at the top of the screen. This function is similar to Window's Restore
function, except it actually works. If you take a snapshot of your known
virus/malware-free installation and later get a virus, all you have to do is
revert to the clean snapshot.

I suggest you read the Help manual that is included with VirtualBox.