I was rencently given a hand-me-down HP a810a with an athlon 64 3300+ (2.4Ghz with 256k l2 cache) and 512Mb micron ram and integrated graphics. I would like to do some gaming so I'm figuring I should probably add memory and a video card.
 
Should I try to stick with micron or can i mix manufacturers? And can I add a 1gig stick to the other slot or should I try to match module sizes? Would I be better tossing the 512 stick and buy a matching pair?
 
Also, have been given an asus n6600le /w 256Mb ddr. Still in the box non-returnable due to lack of reciept. Should I trade up or will it suffice with the aforementioned memory upgrade?

You should be fine mixing RAM manufacturers, just make sure the RAM is the same speed and your new RAM is supported by the HP motherboard (good luck finding those stats). As for the video card, be careful about the power supply. HP (and all OEM's) typically install the bare-minumum power supply in any given machine, so if you install a new video card it may overload it.  
 
Unfortunately, I've never worked with Asus computers.

11/09/2007:  I was searching for a power supply for HP a810n and came across these postings on Google...I have a new graphics card Geforce 7600gt AGP.  I found a power supply that fits perfectly.  It is a 500 watt Antec ATX12V v2.2.  Fits and works perfectly...installed in 15 minutes.  Just remember to break off the 24 Pin to 20 pin for HP a810n.  Just read the instruction..very clear..for a second I thought it wasn't the right power supply but it is.