What type/brand of memory is recommended? I'm planning on at least 512, maybe more.
Go to http://www.kingston.com. They have a memory configurator tool that will tell you exactly what you can do, and what to order, for you Dell.
Newegg seems to have the best pricing - any reason not to go with them?
Absolutely none, even if you do pay a few dollars more than another company. Newegg will take care of you if anything goes wrong.
And a while ago, I was serious about getting a new vid card. After looking at everything under $200, the 6600GT is what I came up with, over anything else.