Possible to mix and match ram sticks? [DDR2-800]

Sure, it should work. However, the RAM in your system will all run at the speed of the slowest installed RAM, and part or all of your memory will be running in single channel mode rather than dual channel mode, because of the unmatched module.
I'd either sell your single module and just use the 2GB kit (best) or not buy the kit and buy a single 1GB module to match the speed/timings of the one you have.

Interesting, why would it resort to running in SDRAM mode? its not because 3gb is an uneven number? :?: Can they be made to match from the bios (same speed, same timings, but possibly different voltages?) and still run in DDR mode together?

You must install memory in pairs to run dual channel mode. As the previous poster explained, you would be better at 2 gig without the 3rd stick.

To answer in order:
- Because of the memory controller design.
- No, it's not.
- No, all RAM in the system is automatically run at the same speed, timings, and voltage; this doesn't affect whether or not the RAM runs in dual channel mode.

You may want to check out the Forum sticky FAQ (especially the link near the end to the excellent Corsair multimedia presentation) to learn more about current RAM technology. This thread contains (among other things) my McDonald's analogy for single/dual channel mode: http://forumz.tomshardware.com/hardware/modules.php?nam...

To clarify for the lurkers out there, SDRAM = Synchronous DRAM and DDR = Double Data Rate, which is a type of SDRAM.

Ok, another Idea, how about buying this... Would they be 100% compatible with each other?

-2x 1gb of OCZ Special Ops DDR2 800 5-5-5-12 @2.1v 195$
-2x 512mb of OCZ Special Ops DDR2 800 5-5-5-12 @2.1v 100$

vs.

-2x 1gb Patriot Extreme Performance DDR2-800 4-4-4-12 310$

Would that give me a total of 3gb of fully functioning dual channel memory? Would these low budget sticks give me better performance then 300$ of high quality 2gb sticks? Low budget 3gb vs. high-end 2gb, which is better?

Yes, the 3GB should work fine in dual-channel mode, but nothing is ever 100% guaranteed. There is also cheaper, better memory available (e.g. http://www.newegg.com/Product/Product.asp?Item=N82E1682... ). As for performance differences, they are likely to be small, but you need to make the call as to what it's worth to you. There are some decent performance tests in this article: http://www.madshrimps.be/?action=getarticle&number=1&ar...

I'm actually kind of in the same boat as to what to do. I need to order more ram since I'm awaiting an RMA to be sent back, but I want everything to be dual channel and at optimum speeds. My RMA ram runs at 4-4-4-12 and is ddr2-800 2x1gb. I'm stuck as to whether i should go same/different brand of additional ram and if i should go 1gb @ 2x512mb or 2gb @ 2x1gb. Either way i would go with ram that is 4cas and can run at 4-4-4-12-2t. I just don't know if the additional money/ram would be worth it beins i'm on xp. Any thoughts regarding speed/value for what i should do?

Because of address space limits, on a 32-bit OS (like your current WinXP or even 32-bit Vista), your system will likely only be able to address about 3GB, so getting 4GB total is a waste unless you are switching to a 64-bit OS soon.