Smokey, I will also add that IMO you would benefit in spending a little extra on an Intel processor. I have many more positive experiences with Intel over AMD over the past couple of years.
First, I'd second the Intel over AMD ... mind you, every pc I've built in 12 years for myself has been AMD ... But in the mass market, your HP, Compaq, Dell, etc.. I would recommend sticking with an intel based system.
Second .. laptops add one function - portability. They loose you the ability to upgrade, the ability to "tinker" and the ability to hold a system longer than a couple of years.
With a proper desktop machine, you may start with onboard video, and then replace that in a year with an inexpensive but decently performing video card. Add more memory, and potentially replace the processor with a faster model. With a desktop machine, should your fancy go that way ... you could even have the potential of having two video cards, with *four* monitors hooked up ... here I sit now, with three monitors in front of me.. one for my main stuff, one to my right for auxiliary functions ... winamp is playing there now, but I often put my Dish SlingAdapter screen there, I can move conversations from chat clients to my left all so that I have enough screen realestate to catch my attention, read something if I need to, but not leave my primary application. Sure you can add one monitor to most laptops .. but in two years, you might have performance issues, running multiple screens and no options to upgrade the video on the laptop.
so if mobility is your greatest need, then yes.. get a laptop, most in the 350 to 550 range will do, get a decent 24" LED based monitor, and go to town..
If mobility isn't important ... then continue down the mid-tower road, and check the specs of any pc you buy to find out that it is expandible.
A key term to look for, to see that a machine *is* current technology ... DDR3 memory. DDR2 is very common, and given two systems similarly equiped ... I'll take the DDR3 machine over the DDR2 machine every time.. if its dual core now.. 99.99999% chance it can go quad core when I want or decide to afford it to.
EDIT: here's a link ... you just need to go through the first two pages to get a basic understanding of the cache differences between AMD Athlon II and Phenom II
Athlon II Or Phenom II: Does Your CPU Need L3 Cache? : L3 Cache: How Important Is It To AMD?
that second page, also gives a comparison on cache memory between Phenom II and Intel Core i5/i7's.
if you're going for prebuilt ... core i5 better than core i3 but not worth 200 dollars more.. maybe 75 to 100.
Clarity is always my most important goal too. People ask questions to get the best possible answers in order to make the best possible decisions. I always try to provide them with the best answer to my knowledge and hope that others do the same when I ask questions (which I do a lot on this board) 
