Damn...I've been out of work for almost four years and this frickin' pager keeps going off!
This one is $349 after rebate...comes with a 17" monitor AND XP however...I dont think you'll find a good new machine for less without them. Not a good system for "first person shooter" type games as the graphics subsystem is more quality than speed, but other than that, it looks like a good machine. I havent seen these Dell 3000 series, but the 2400's they replace were very good for home use.
Donate the old monitor or sell the new one...probably get $40-50 for it...and he can probably sell his old copy of XP as well for $50-60. The copy of XP that comes with this one is probably an OEM copy and is bonded to the machine.
Doesnt need much, maybe a modem or whatever other goodies he needs. Extras are generally pretty cheap when ordered WITH a system, so consider carefully.
You can also do a Wab and snoop through the refurbished/clearance section for slightly cheaper models with no monitor. Unfortunately they just had a HUGE clearance sale and there are only a couple of units in stock...only thing cheaper than the above machine was a 2.2GHz celeron machine for $309. The new machine above comes with a free upgrade to 512MB ram and 80GB disk, a bunch of software, 2 year warranty and six months free AOL or Earthlink. Pretty good deal.