First off, you would need to increase your 256mb of RAM to atleast 512mb, and preferably 1 Full Gig. Using Windows XP-Pro is important as well . . . What kind of a broadband connection are you using, and what is the current download speed you are getting?
The reason I ask these questions is because there are some "latency" issues regarding being a remote trader, as opposed to trading out of an office and using a platform that is connected directly to a server. You need to make sure that you are on an even playing field from a Hardware standpoint before you then get involved in trying to decide which trading platform is the best for pure scalping.
For sheer speed, Assent's "Hammer" is probably the fastest trading platform for scalping. However, if you are into using charts, the charting on Hammer will disappoint you and you will have to spend another $165.00 per month from a third-party charting vendor like Realtick or E-Signal.