I would get a Quadro card for AutoCAD since it can do rendering on a GPU; a GPU will speed up rendering the complex stuff.
Since you need Windows to run it as well, I'd stick with buying a PC for this job; sometimes it's not good to go with a Mac, and this is one of those cases.
His dad is only doing 2D rendering (with AutoCAD 2004. While 2004 had 3D rendering 2008+ added the
good rendering stuff.) Also, they are on a tight budget. I know there are some "low"-end Quadro Cards, but they'd end up adding unnecessary expense to the rig for practically zero returns. I've run VIZ/3DS on a Radeon x850 XT 256MB and a GeForce 7800 256MB.
If you're going to go the PC route, seriously, just buy a mid-range Dell or HP tower with XP installed on it. Core2Duo 2.0+, 2GB RAM (4 if you're feeling generous) and a 160-320GB Hard Drive. If you really feel spendy, configure it with a Radeon or GeForce Card. Buy the 3-year warranty on it. No offense to anyone else, but this is a business tool first and foremost. Any time spent configuring or building is time not spent working and earning money. And buying too high spec of a machine, or new software (especially something like AutoCAD) is spending money that could be spent elsewhere. When the economy picks up, buy a new Mac Pro and AutoCAD 201x if you feel like it.
Please note that I'm not trying to come down hard on anyone. Please don't take it that way. I have been drafting for 9+ years, so it's not like I don't know what I'm talking about. I'm just trying to be practical/realistic here.
</rant>
</get off my lawn>
</only 27 years old>
By the way, here are the System Requirements for AutoCAD 2004:
* Intel Pentium III or later, with 800 MHz or faster processor, or compatible
* Microsoft Windows XP (Professional, Home Edition, or Tablet PC Edition)
* Windows 2000, or Windows NT 4.0 (SP6a or later)
* 256 MB RAM
* 300 MB free disk space for installation
* 1024x768 VGA with true colour (minimum)
* Microsoft Internet Explorer 6.0
* Mouse, trackball, or compatible pointing device
* CD-ROM drive