If that 1gb in your sig means ram, up that- max it out if it isn't already. Perhaps you can get another gig in there. I'm surprised to hear your pc is chocking with RT's. How many tracks does it take to start the problem? Plugins I can understand- that's where it can be taxing. But straight RT's shouldn't do that unless you have 20 or more tracks going. It sounds to me like you have a very low buffer rate set. Make sure in your sound card and your audio software that you have a higher buffer setting set. The only time you need a very low buffer setting is when you are recording and monitoring playback, or playing virtual instruments live with a midi keyboard. You want a low buffer setting so you have as little latency as possible. But just throwing up RT's and mixing should not be a problem. Your pc specs aren't THAT bad or old. Studdering and grinding to a hault points to low buffer settings. Raise them up incrementally until you have smooth playback. I'm not saying a new pc is a bad thing, but you should be getting more out of what you have already if things are set right.

Dan