xp upgrade and how to dualboot

ive got an 8gb intel core2 quad Q6600 2.4ghz system running xp sp3. i recently discovered after a virus latched itself to the system that windows only recognises 3gb of ram and the other five are sitting idley in their slots. this may have been the case before the infection but as i said i only noticed it after as the computer was a hell of alot more sluggish when i was making a track in nuendo. after recording maybe 6 parts the cpu level started to peak and i got the dreaded glitching noises indicating that the cpu/ram was being overworked. this was the first time it happened in the 7 months that ive had the pc. before that i could layer 30 parts at a guess running realtime effects and the cpu meter barely moved. so now im thinking about upgrading to a 64 bit os to utilise the whole 8gb of ram.
what might you suggest in terms of os? and also do i need to upgrade all of my other software to 64 bit or will it work fine as they are?
ideally id like to update the os to 64bit without having to update the rest of the software as it will take at least a week to do so but if its not possible then ill have to settle with having just 3gb of ram.
is there any software i can get that will allow windows to use the whole 8gb? and failing that could i set up a 64bit os to dual boot and then use the already installed production programs with the 64bit os?
sorry for the lengthy post but i wanted to get the most out of any response i may get.
thanks for your time.
sincerely

Frustrated Producer!

 

My main concern would be the fact that it worked properly before the infection and not now, I'd address that first before even thinking of moving to 64bit. Yes, you'll then be able to access all your RAM but at what cost? A dualboot is easy to set up but you'd still have to install your applications again and as XP X64 does not have a trial anymore, you'll have to buy it first, sight unseen. Vista X64 would be an even greater leap for your applications, if they'll work or not.