RAM confusion

I recently ended up with a 2006 Mac Pro and 20" Apple LCD. It looks very nice, but it was not enough RAM so I upgraded to 8GB.

Full specs:

-2x dual core 2.66GHz CPU

-GeForce 7300

-750GB HDD

-OS X 10.6.whateverthelatestupdateis

when I got it originally it had 6x512MB sticks. I bought 8x1GB off eBay and installed them. However, they were running very hot! I could not touch it!

I think the problem is that the ones I bought go not have the big heatsinks...

I bought two sets of this for an 8GB total:

http://www.ebay.com/itm/120912671880?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m143 9.l2649

SO... I plan on doing a lot on this computer such as leaving it on 24/7 running folding@home, etc. It might also eventually become a web server or something I don't know. But I need 100% rock solid reliablility and these hot memory modules concern me.

Now, what I really need help with is that when I put 6x1GB in, it only recognizes 4GB. WHAT!!!? I put 3 in the top memory riser and 3 in the bottom memory riser!

Why? I am OK with 6GB (will sell the remainer) and am going to put the big black heatspreaders from the 512MB modules onto the 1GB modules and vice versa. That way I can have 6GB RAM AND 100% RELIABILITY.

Please tell me why it only works as 4GB though? Thank you.

Message was edited by: shovenose