If at all possible, I would take a computer savvy friend with you to purchase a new system - especially at Best Buy. They can be overwhelming. My mother-in-law (with our help) just bought her new computer at OfficeDepot. It has a 19" flat screen monitor and a super processor. Printer,scanner, copier was almost free with mail in rebate. No Vista. It was a good deal I thought. We wanted to make sure she got what she needed and got a good deal. It's good to have a few opinions also.
I have a 15" flat screen monitor and a printer, scanner, copier (this is soooo nice). I would get the fastest processor you can afford. I run Photoshop 7, Quark, Illustrator 10 and many other huge programs but mine does seem to do fine - kinda slow though. My system is a couple years old. I don't have Vista and don't really plan to upgrade in the near future. Do invest in Norton or some virus protection. Any computer should come with a free trial version for 30 days I think...
Hope any of this helps.