[est1895]

I currently have 2x1gbs sticks.  They are PC2-6400 running at 400mhz.  Now according to Kingston, both sticks should run at 800mhz.  Since I am switching to Windows7, I need 2x2gb sticks more. Here are my questions:
1) Can they be another brand name?
2) Do they have to be the same latency or volt?
3) Does anyone know where I can get some old Kingston HyperX 2x2gb sticks?

[MP-Ryan]

Yes, it's a good idea, did you try NewEgg or Amazon?

[est1895]

Newegg says they are not selling them anymore.

As for Amazon or Ebay, how do I know that the memory is any good?

Now I did find them at Best Buy, but they want way too much.  I need find them 'cheap'.  The reason why is, " I can't wait for my old system to crash so I can upgrade."  In other words, this memory is only needed for a short while.

Yes MP-Ryan, at eBay I can get a used one for only $15-$20 for one, but for a new one eBay wants $33 and Amazon is far more expensive that eBay.

If anyone can help, please do. 

[Klaustrophobia]

no, they don't need to be the same brand.  if it's easy to match, never a bad idea, but far from necessary.  you should try to match speeds and latencies, but also not absolutely necessary.  you'll just have to run them at whatever the lowest speeds and highest voltages are in the set.  which your BIOS will in all likelihood do for you as long as the settings are in auto.

anything in this list should do.
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007611%20600006042%20600006066&IsNodeId=1&name=4GB%20%282%20x%202GB%29&ShowDeactivatedMark=False

but just as a general rule, avoid things that include "value" in the name, since higher quality are never more than a buck or two more.

as for the speed, you multiply the actual clock speed of the ram (the 400 mhz you saw) by two to get the advertised speed (800 mhz).  DDR = double data rate.  yours are running properly.