You have 1 stick of 512mb,you do not need a pair as I doubt you run dual channel Ram on a P4 of that vintage. Are you sure about the PC 2700? You can get youur puter to tell you what your 512 is. New Egg is great,best price,fast shipping-there are even reviews which give useful clues as to what sucks
I often have a high speed DSL fed window or 2 open while making cover art in photo impact and converting flac>wave in dbPower amp,can't do that with auzeris,but with Bit Tornado often have 2 windows running and doing graphics or conversions....and that's with 64 mb of slow old Ram. Get a faster HDD,you have enough RAM unless doing heavy Photoshop and multiple downloads. The difference between a 5400 rpm drive and a 7200 rpm is significant. Ideally you have 2 HDD's,one where your torrents-flacs-waves,live,another where the OS,Software live. One drive is writing your incoming torrents uninterrupted,the other is doing the other stuff,uninterrupted

...also,it is not your CPU's memory. The CPU has a "cache" a built in fast-access memory,and it is relatively a lot smaller and can not be added to. RAM is more like system memory,or the motherboards memory. Adding RAM is rather easy BUT learn abot anti-static precautions. Not handling the typical computer internal parts correctly can do damage. Otherwise,HDD or RAM is easy,15 min stuff.