Would these 2 memorys mix well

I wouldn't reccomend mismatching any of your memory. It might cause system instability, or incompatibilty. Although the timings are similar, a spec here and there in the spd might give you some compatibilty problems. Especially being different size ram, you're best bet is to go with what you already have, if planning to upgrade.

You make mention of different size ram being an issue.. What if the two different ram modules were the exact same ram from the same mfg, but one modules was a 1gb (2 x 512) and the other was a 2gb module (2 x 1gb) ? Do you think that would be inadvisable also?

And I asked a similar question, too, over here: http://forumz.tomshardware.com/hardware/mix-quantities-...

Seems like its a hot issue for alot of folks.. Makes sense, cause Im sure alot of people, like me, maybe equipped their mobos initially with a 1 gb (2 x 512) ddr2 module, but then decided when it came time to fill up the additional pair of empty slots, maybe cause the ram price came down significantly, whatever, to fill them with a 2gb (2 x 1gb) ddr2 module, creating a new total of 3gb ddr2 ram..... The answer to my post on this was to go ahead and mix the sizes as long as the mfg, speed, timings, and model numbers of the ram type are the same. Of course, 'Ram Guy' at Corsair advises against mixing even the module Sizes, claiming:

"Adding 2 x 1 GB modules to your existing 2 x 512MB will most likely not be stable and is not recommended. The ICs used for the 512MB modules are different from the ones that are used in the 1GB modules. In order for the system to be stable all the RAM needs to be in sync, and all the ICs on the RAM need to be exactly the same. Since the ICs are not exactly the same on these 2 different sets of modules, there may be instances where the RAM gets out of sync (even if it is in milliseconds) and this can cause errors and crash your system. It is NOT recommended to mix and match any modules together on this platform as it can cause many problems. My suggestion would be to add only what you currently have in your system to the exact part number or replace all the modules with new ones. Sorry about that."

Most posters here say hes full of Sxxx! So, Ill probably go with them, and not the Corsair rep..

[quote="StevenT"]

yah, I hear he's an idiot too. lol To be fair maybe he just says things based on company policy.

Actually I'm doing it different than you.. Addiing 2 512's after already having 2 1gb's. heh. Should be more thrilling for you to suddenly have 2 extra gb's though! lol

Yea, so, if youll be doing your addon before mine, let me know how you make out. Unfortunately, the 1gb module IM using is Corsair XMS2 PC2 6400C4 ram, which $95 just for the 1gb module, which is one of the more expensive 1gb dd42 PC2-6400C4 modules around. The 2gb version sells for $180!! But, at least, there's a $50 mail in rebate which helps.. Of course, its currently OUt of Stock at newegg!!

Exactly right.
The other issue is that some MBs (especially el cheapo ones and ones with lower-tier chipsets) are only marginal in their support for 4 DIMMs installed.