I'm not able to understand well your statement regarding the video card. Are you mentioning that the card was ok on a previous computer but when installed in this computer the PC has been bugging out? Have you switched it back to the previous computer to see if things remain stable on that computer as well, and if the victim PC stabilizes without the video card?
Just so you are aware, Compaq - as well as many OEM PCs - are designed with very cheap components and usually only enough to keep a system stable for a minimum amount of time with the default configuration. This is especially true with their PSUs (power supplies), which usually are designed only to handle default configuration and - like any PSU - will degrade in wattage output with age. There is a very, very good possibility your new video card is overtaxing this system's power supply beyond its capacity.
Other than that, I cannot explain about this any further beyond what's currently available from the data. I can say that the erratic pattern, as well as other signs such as missing bits in CPU registers, all point to hardware failure of some level. One cannot really deduce what exact hardware is responsible from crashdumps, but there are hardware tests that can help. I recommend you do the card swap first to see what happens when this PC runs without the new card before going for tests. If the card itself goes great on one PC but it causes another PC to go unstable, than I have to point blame at an insufficient (or bad) power supply.