Is my Dell XPS-400 running at half-speed?

I have a Dell XPS-400 and an older Dell Dimension 8300; both PCs run
Windows XP Pro SP2; both machines have more than 1GB memory. I've
noticed that some games appear to run much slower on the newer XPS-400
(which has a Radeon X300 with 128MB of on-board memory) than the older
8300 (not sure of the video card).

One thing that I noticed is that if I use software that tells me how
much CPU "power" routines are using, on the XPS-400 no routine seems
to go over 50% (except for System Idle Process) -- while this is great
when undergoing an antivirus scan (so I at least have a half-powered
machine), there are times I want to devote 100% of the CPU to a
task/service (like a game, or an emulator). I suspect that this is a
case of having two CPUs but not having them both devoted to aspects of
the same task. [These two machines are in two different cities, so I
can't "query" the 8300 right now ...]

Any hints on how (or if it is possible) to get 100% effort from this
PC?

 

You can get two processors working on the same thing only if the
software application is designed and written to do it.
Most tasks don't have an obvious way to do them on two processors, and
so they won't get written that way. The essential problem is that
usually the future path of the program depends on the result just
obtained, and so everybody has to wait on each result before anything
else can be done. You can do waiting for a result as fast on one
processor as on two.

On the other hand, unrelated tasks can be done at the same time without
much difficulty at all, which is where the speedup comes from. The one
task doesn't have to wait on the other's results and vice versa.