Hi muplayer and welcome to the forums
I have had a look at the manual for your motherboard (you may need to refer to this to follow this post). You state that you are using DIMM1 and DIMM4. You should be using DIMMs1 and 3 or 2 and 4 (i.e. both blue or both white sockets). Make sure that all settings in your BIOS are set to 'Auto' and that the FSBSEL jumper is on pins 1-2 (default). Check that your graphics cards are in the correct slots.
Leave the side off your case and when you next start your system, enter the BIOS and select 'PC Health Status'. Keep an eye on this, and also keep an eye on the 'Onboard Debug LED'. If your system seems stable after 20 mins or so, reboot into Vista but don't run any programs. Again, monitor the LEDs. Next, run some programs and install other programs whilst monitoring the LEDs. Please post back with any codes shown on the LEDs and what you were doing when they appeared. If you get a code appearing whilst you are monitoring the 'PC Health Status', please enclose the readings from that as well.