I've just arrived back in Ireland and will be away from my Mac for the next 2 weeks (but the Apple factory is just up the road
As to FinderPop creating that null process, that would be news to me.
Back in the day, the (null) process was OS 9 running in Classic mode! I take it you can definitely rule that out? FinderPop hasn't launched Classic to open your document, has it??
I don't think I do anything special, from what I remember I just ask the Finder to open whatever it is you selected. Or it's possible I might use Launch Services to open it, I can't remember right now but will have a look at the code and report back later (the code I'm talking about probably won't have changed in years.)
What happens if you control-command-click in that folder and from the resulting FinderPop "Contents" menu, select your .doc or .xls file? Do you still get a (null) process?