Unganged mode for your memory configuration is better than ganged-especially when multitasking. Ganged will mean that the two memory controllers will aggregate rather than act independent, which is unganged. Some test will show what may seem an advantage to ganged mode, but this is due to the lacking support for this mode in benchmarking.
Also, luckily, most of your BIOS options are automatically enabled. To note, if you are to use 32bit you show change the MTRR (memory mapping) to disabled. This should only be enabled if using 64bit.
Clear the CMOS and leave the memory at the default auto setting. The manual says the default for IDE prefetch mode is disabled, looks like a typo, make sure this is enabled. AHCI mode is the preferred mode to interface your HDD. Enable and follow the instructions for installation. You can update the drivers after install, easily (this has been touched on already I know. But you cleared the CMOS to start from scratch correct?). I would also disable Hybrid SLI, HDMI audio since not using the integrated graphics, 1394 if not in use, and serial port. Change the suspend type to S3 only. Last thing change the power up on PCI/PCIE device to enable if you want to use wake on LAN or allow a installed device to wake the PC. To note, the integrated graphics will automatically disable when it detects a video card, according to the manual.
There is nothing wrong with 64bit, but it can cause what is inherently wrong with the hardware to surface if there is a problem with it. Having install problems like you say will always point to memory. This is not perfect but may help identify: http://www.memtest.org/
My 2 cents..hopefully gets you somewhere.