I have 2x1gb sticks of A-DATA ram currently but I think more would be useful. The only problem is I can't find the exact same ram again. I know your not supposed to mix ram but if I got another 2x1gb sticks of A-DATA ram with the same voltage and timings would it work. I don't need any more ram but I think I could get my machine running a bit more efficiently if I had some more. I'm currently running vista 32 bit (and know it won't use it all), but I'm going to switch to 7 64bit next year because I'll get the student discount.
Yeah, matching the speed (data transfer rate), timing and voltage is the thing to do if the same RAM is not available. The BIOS sets the three parameters. The DIMMs having the same voltage requirements, etc. should be good to go. Four DIMMs are drawing more voltage than two. If any instability occurs, try bumping the voltage a bit if the BIOS has the adjustment available.