Thought I'd touch base and let you know what the results were.
In our originial logs, the user had some really borked registry entries which appeared to be mutilated by malware. For example:
HKLM\...\Run: [DellSupportCenter] TER
Where the file name had been "chopped off" for lack of a better term, and yet the system was still functioning. When I ran tools on the machine, I'd instructed them to leave these entries alone and not to remove them, since I didn't know what the effects would be.
We had previously run Windows All in One (without an issue), and were down to an internet issue (internet working but red X persisting on connection in tray). We'd run another automated services repair tool without problem, so I decided to run Windows All in One again. This time, the graphics driver went - and I suspect it was probably something that was in one of those apparently orphaned but functioning registry entries that I'd previously left alone.
After considering pulling files off with Puppy Linux, the user decided they had sufficient backup, did a repair of Vista, upon which graphics came back but networking issue persisted. They had original driver disc for Vista - installed an original Dell driver and it finally fixed the remaining issue.
So long story short - we are finally able to get back to business now on this machine.