My Vista (64 bit Ultimate) hates my ram. Whenever I try to add more than 2 gb (I have 4 2gb sticks), Vista gets veary unstable as in locks up or randomly reboots. I've tested each ram module in my old desktop, they all check out. I also installed the KB 929777 update which was supposed fix some RAM issues, but it didn't help. My vista fully up to date as is the drivers to the rest of my components.

nice dude 8gb ram is great but vista is still having problems and microsoft is trying to fix them so they will have a souluution for you some time

Try these:

Windows Memory Diagnostic Tool

Memtest86+

Are these all the same modules? If they are different brands there may be a conflict or the RAM itself may be bad.

I am running Windows Vista 64 with 8 gig of ram works fine on my end, Running (ASUS P5K DELUXE/WIFI-AP LGA 775 Intel P35 ATX Intel Motherboard), (BFG Tech BFGE88768UOCE GeForce 8800Ultra 768MB GDDR3 PCI Express x16 OC HDCP Video Card), (BFG Tech BFGR1000WPSU ATX 12V 2.2/EPS 12V 2.91 1000W Power Supply), (Intel Core 2 Duo E6700 Conroe 2.66GHz LGA 775 Processor Model BX80557E6700), (2 Western Digital Raptor WD1500ADFD 150GB 10,000 RPM Serial ATA150 Hard Drive), (2 Seagate Barracuda 7200.10 ST3500630AS 500GB 7200 RPM SATA 3.0Gb/s Hard Drive) , (Logitech G15 Gaming Keyboard), (BenQ FP222WH Black 22" 5ms DVI Widescreen HDMI LCD Monitor), (Sony NEC Optiarc 18X DVD±R DVD Burner With 12X DVD-RAM Write Black E-IDE / ATAPI Model 7170A-0B), (Creative 70SB046A00000 7.1 Channels PCI Interface Sound Blaster X-Fi XtremeGamer Fatal1ty Professional Series), and the memory i am running is (Patriot eXtreme Performance 4GB(2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model PDC24G6400ELK), I am running as i said 8 gig of this Patriot Memory so far no problems. going to get a quad core as soon as the price drops july 22, 2007.