It's certainly TRUE that Windows VISTA is a huge resource "hog" but I think that you are really behind the curve technology wise in that 512kb of memory is not acceptable to run a trading platform, nor is your processor capable of keeping up.
I have a 4.5 year old Dell 8300 with a Pentium 4 at 2.6 GHz., and 2 Gigs of memory and I am able to keep up pretty well on a Broadband line that "averages" around 3.5MB per second clear across the country to my broker's quote server.
That having been said, I know that my L2 cache is pretty weak compared to the latest Duo-Core processors that are running 4 MEGABYTES of L2 cache. I believe that I have something like 512kb in my L2 cache ( which is like a mini-memory ).
This is key.
As a result I just ordered a refurbished Dell computer with a Duo-Core 3.00 processor with a 1333 front side bus and 2 gigs of PC-6400 RAM at 800MHz. for a little over $500 on the Dell Business Outlet site. Comes with Windows XP and a 1-year warranty like the new Dells.
My guess is that your microprocessor and its cache is totally "overloaded" and in need of being replaced. In fact, I just looked up the stats of your microprocessor and it appears to have ONLY 8k of cache!
Furthermore, your microprocessor only has a 400 MHz front side bus. Compare that with my Pentium 4 at 2.6 GHz that has an 800 MHz bus, while the new Duo-Core processors are running with a 1333 front side bus!
Your computer is certainly holding you back. There is no way that it can PROCESS today's quote data, especially since the Hybrid system has swamped trading platforms with triple and quadruple the data. We are talking about 60-80,000 UPDATES PER SECOND NOW!
You might also wish to do a trace-route ( via the DOS prompt ) back to the server you get your quotes from and see what the "latency" is along all of the transfer hops on the Internet Superhighway.
If you are over 100 milliseconds, that would be bad. If you are in the 80's, that would be good.
Cleaning out unnecessary "Temp Files" that have clogged up your hard drive can also help a bit ( go to Accessories>System Tools>Disk Clean-Up )
But in all honesty, your microprocessor's super small L2 cache, lack of processing power, and memory is really holding you back, regardless of how fast your internet connection is.
Hope this helps.