I agree about the use of RAM other than Dell. Their computers are fine. I have one. But they overcharge big time for add-ons. And they're not really any better than other brands. They obviously don't make their own RAM. But it's also true, as has been said, that you must make sure that whatever RAM you get is compatible. You should be okay since your system is new. But I'd take richtraders advice and pull a dimm out and bring it in to where you will get the RAM or if you buy it online, make sure it will be compatible.
The other issue regarding this is bandwidth. You can have the fastest setup going and if you have a slow dialup connection, like I do now (unfortunately I'm in a temporary situation where that's the only option -

) you're not going to be able to run anything well. I have a 3 yr. old Dell with a 500 mhz Pentium III and 384 mgs of PC100 DRAM and it runs fine offline. But due to my slow dialup connection I've been having major hassles lately trying to run all my data feeds well. I just installed a very fast 120 gig, 8 mb buffer Western Digital hard drive with Win XP Pro. And I just switched brokers and am back using RealTick 7.6 and I also run eSignal and usually several mIRC live trading rooms, plus a couple of browsers, occasionally TC2000, and Photoshop, etc. And actually before I switched I was running Win 98 SE and had an account with CyberTrader and all these applications ran fine even on my slow connection. I'll probably upgrade my main board and buy a faster chip and add more RAM here soon, everything being so cheap these days, and also because I do a lot of graphics work. But the bandwidth issue I think is probably the most important factor in your being able to run all your applications well. That and RAM which you seem to have plenty of for trading, especially since it's RDRAM. Good luck. Let us know how you do.
Here's a good link in regard to this, The Kingston Ultimate Memory Guide
http://www.kingston.com/tools/umg/default.asp
P.S. I had always heard that Micron was behind jacking up the prices of RAM in the mid 90's and then they had that investigation recently accusing them of just that. And Rambus was trying to manipulate things too so you'd be forced to use RDRAM. Maybe they'll be more reluctant to do this going forward. We hope so.