So this is a home-built with a MSI Neo2 915P motherboard and a radeon x550 video card.
The error is either a hardware conflict or related driver conflict.
If you have already downloaded all the VISTA drivers for that board, including BIOS, Chipset, and the like, and upgraded the driver for the Radeon X550, then you still have memory to discuss, as well as the sound card...
The Problem with VISTA installs is that the error could be anywhere... since the drivers were not always correct.
You can learn a lot by closely examining the Device manager for any red or yellow flags next to any devices.
Then go to Event Viewer and look at the error lists there... Start->Control Panel->Administrative Tools->Computer Management->Event Viewer.
Those two looks should give you enough information for your next step.
If it were mine, I would just install Windows XP Professional and forget about VISTA