I have 2 Gig of RAM but seldom use 1 G.
That's not particularly surprising. 2GB of RAM is *way* more than most
people running XP can make effective use of. Despite the advice of
those who say that more RAM means better performance, that is true
only up to a point. 2GB is considerably past that point for almost
everyone.
What apps do you run? Unless you do things like video editing or
editing large photographic images, even 1GB is way more than
necessary. For normal business applications, most people see no
performance gains by going past 512MB, and often even 256MB is enough.
Is there a way to force a prgram to
use all of the available RAM and increase performance?
No. How much RAM a program uses depends on the size of the program and
the size of the data files it is using. You can't change that, and
even if you could, it would not increase performance.
Note that the CPU
usage does often use 100% of the CPU
That's a different matter entirely and unrelated to RAM usage.
However, if CPU usage is often 100%, something is seriously wrong with
your system, and I suspect that you are infested with malware.