I need to know the codec you used, not the program.
for the system specs,
get cpu-z
and post what it says for processor name, core speed and memory type (memory tab)
just because I'm curious...keep windows task manager (what comes up when you press ctrl+alt+del) open and open vegas. If the numerator of the commit charge gets really close to the denominator...then your problem is that you don't have enough memory.
In that case there are a few things you can do (in addition to getting more ram)
but it would be easier to discuss that over MSN or AIM