You guys are mean
to stray desktop newbies around here. First Alienware, then overclocking?
Fry the budget or the CPU, it's all the same...
Seriously though, damn near everybody who's posted has given some good advice. My 2 cents:
The newest generation of AMD chips kicks Intel's butt on everything but the absolute lowest end of the scale. I don't know how well AutoCAD or whatever you're using can take advantage of multiple processors, but the dual-core chips that AMD makes are much more efficient than Intel's when the code is written to use both. For gaming, AMD has a slight to moderate lead, unless you're playing F.E.A.R. or some of the other very new games. In that case, once again, Intel is the kid getting a wedgie on the playground.
As far as RAID goes, for your very first foray into the do it yourself world, here's some basic do's and don'ts:
DO get a nice, big hard drive. Maybe even two.
DON'T use a RAID system.
If you want a 600-1000 gig storage solution, put two drives in there, making sure before you buy that they're compatable with your motherboard. SATA to SATA, IDE to IDE, never the two shall meet unless you want to complicate things.
For online research, Wikipedia ( http://en.wikipedia.org
) is your friend. You should be able to bounce all over the place from article to article until you understand the basics of a PC's gizzards. For a weighty, thorough offline tome, "Repairing and Upgrading PC's, 17th edition", is on my list for the next Amazon.com shipment. Kinda pricey, but it doubles as a home defense system when balanced above your front door.
Finally, how digital savvy are you, Pinpoint? Do MP3 players more complicated than an Ipod scare you? Did the neighbor's kid set the blinking VCR clock in your house? Does the word "RAM" conjure up images of sheep or something you can't get enough of? (If both, seek help.)
When I built my first PC, I had a pretty good idea of what went inside, but I hadn't actually done much tinkering before. I looked around, asked questions, grabbed an OEM copy of Windows 98, then waited for a beautiful Saturday summer afternoon I could spent soaking up the air conditioning and fluorescent lights. As long as you're careful and grok the geekspeak, putting together a desktop PC is only slightly more difficult than assembling a Lego model. Most pieces only fit together the right way.