Welcome to the Forum
Since no respopnse so far, I'll have a go.
1) The only Capture Device I use is my DV Cam.
2) I assume that your Pinnacle BOB has the option of Capturing both AV & DV.
3) Since both VIA OHCI Compliant IEEE 1394 Host Controller & presumably your Cam is showing (when connected) in Imaging Devices, in Device Manager & Cam is recognised by Studio & you can capture intermittently, IMO you don't have either a Software or Hardware prob, except for possibly a faulty Firewire cable. Therefore:
4) Try Capturing in WIndows Moviemaker, to test the cable, using another Prog. If no go, it's possibly your Firewire cable (See below).
5)
change the display resolution upto 800x600 with lowest refresh rate possible
IMO, that wouldn't have any effect. However Disabling High Resolution Preview in S12 would & Disabling S12 Preview & viewing via Cam's Viewscreen would be better.
6) Defragment your Hard Drive
7) Do both a File System Error & Hdd Error check. I don't Have Vista, however the route for XP would be:
8) Start / My Computer / Right - Click on Capture Drive Icon / Properties / Tools / Error Checking / Check now & do both sequentially, in following Pop-Up.
9) Do 6), 7) & 8) first.
On balance, it looks as thougjh you have a faulty Firewire Cable., since it has 2 data transfer signals. One for cam recognition & control, which seems to be working & one for Video (with embedded Audio), which doesn't seem to be working.