It's simple...task manager...performance tab--shows ram usage.
You don't really mention your OS specifics...4gb if 32bit may not even be being utilized. More accurately--it is NOT all being utilized--the only question is to what degree. The max I was able to squeeze out for a user mode app was about 2.8gb in 32bit Windows--and that was with customization to make that happen.
You're not running out of CPU unless maybe you have the buffers set to 32samples or something. My full string arrangements with impulse verbs, etc, don't eat 25% of my c2quad at 128 sample buffer. I Ran the original VI for years on a single core P4/4gb machine. VSL OS not CPU intensive. Now, of you're opening play or Kontakt4 libs in VE, that changes.
What you want to do it to be looking at task manager in real time while you have the arrangement playing back. Do you see CPU(s) spiking? If you're out of ram, that will certainly cause it...but, that's easier to determine than fix if 32bit OS.