Loose rivets,
I have alomost the exact configuration you listed:
AthlonXP 2800+ (Barton)
Abit NF7-S Rev.2
1GB OCZ RAM
ATI Radeon 9800 Pro 128MB
2 x 80GB Seagate SATA hard drives in a striped RAID array (sorry Richard, the Raptors are still too expensive up here
)
It's worked very well for me so far. I use and Audigy2 ZS sound card as I don't have speakers that can use the SoundStorm audio (you need speakers with digital input) and the onboard analog output sucks. I might get the Creative DDTS-100 to solve this problem someday though.
I'm not sure about that Asus board Richard mentioned, but some of the new nForce 2 Ultra motherboards have native SATA, Gigabit Ethernet and a built in hardware firewall. You might want to check them out.
MS Flight Sim will probably be harder on your computer than AutoCAD will be. Unless you're into rendering huge photorealistic computer models.
goates