The lap top downstairs can no longer access the wireless printer in my office.  Please advise on the fix.

If the laptop downstairs was getting to the printer by the mac pro having shared the printer over to it, then it would best to have the laptop establish it's own wireless connection to the printer.  

G drive is gone again (my backup).. the pc is showing it as a Z drive.  I know you fixed this once.. so tell me how to do it, if you think I am capable.

You should be able to toggle the use of all USB devices by using the toggle switch in the bottom right hand corner of the parallels window.  If you don't see it there, try plugging it in once Windows is booted and you should be prompted to choose which operating system is to assume control.  Remember that once you quit windows, the devices that were being controlled by parallels (Windows) will fall back to the Mac.  ie:  CD's, flash drives, external HD's.  

I am about to install the software to put the new printer on the MAC  side.  I assume this is just the normal process.

Yes.  You can go download the latest drivers from the web site or use the install disc that came with the printer.