Dear Brian,
good question.
Here is the Asus QVL for the Pk5 (the Pk5 E does not have its own QVL that I could find)
http://usa.asus.com/100/downlo...ducts/1749/1749_10.pdf
Here are all three of them on Newegg:
http://www.newegg.com/Product/...8076%2CN82E16820148144
With this first model #, you can fill all four slots, according to Asus:
DDR2 800 1024MB Crucial Heat-Sink Package 4 N/A DS BL12864AA804.16FD V V V
With these latter two, only two slots:
DDR2 800 1024MB Crucial Heat-Sink Package 4 N/A DS BL12864
AL804.16FD3 V V
DDR2 800 1024MB Crucial Heat-Sink Package 4 N/A DS BL12864
AA804.16FD3 V V
On Newegg, here is one set of Ballistix 2 x 1GB with that product #:
http://www.newegg.com/Product/...x?Item=N82E16820146565
And another with the AL in the product ID #:
http://www.newegg.com/Product/...x?Item=N82E16820148076
"L" means "lights", as in LEDs?
So that eliminates the AL model...
Differentiating between the two AAs, one with the 16FD, and the other with the 16FD3 extension??: I think it's the LEDs.
So, I think this is the one you can use four of:
http://www.newegg.com/Product/...x?Item=N82E16820146565
I did notice this interview with Rahul Sood of Voodoo/HP, wherein he pretty much rips Crucial memory--surprised me that he named names, as that is unusual in this day and age:
http://www.rahulsood.com/search?q=crucial
I believe there is no better enthusiast memory manufacturer than Corsair. Corsair is known for their quality and consistency, and when we experience a problem with their memory they do everything they can to get us up and running in short order. We have tried all types of performance memory, including Crucial, Kingston, OCZ, and many others ? and there have been times when we tried to switch ? but we ended up returning to Corsair.
I remember one time we were using Crucial Ballistix memory and almost every single freaking chip we sold ended up being returned, sometimes more than once. It was a total disaster, and there was really no explanation for it ? although we believed the memory was unable to handle the high voltage they were designed for. Props to Crucial for honouring the warranty, but the cost incurred by Voodoo was insane and unacceptable; although we probably wouldn?t have switched to another manufacturer so quickly if they had not tried to convince us that we were the only ones experiencing such problems.
Since then we switched back to Corsair and haven?t looked back.
For four GB of ram, maybe consider one of these? Two sticks are easier to get stable than four I think....
http://www.newegg.com/Product/...0227%2CN82E16820104001
HTH
NXIL
Edit: spelling