I too have an aging PC, the motherboard/CPU is the same as yours IIRC (MSI K7N2 Delta-L, Athlon XP 3200?). I decided to take the plunge and buy a new machine as the cost of upgrading the guts was the same sort of price as I could buy a new base unit from the Dell factory outlet. These are refurbished returns, with full guarantee, and come without monitors - I too have decided to keep my CRT instead of switching to flat panel.
I seriously considered a mac as my primary use is image editing. But the cost of a new mac was double the price of an equivalent spec PC, plus I'd have the cost of having to buy new software applications. It was this extra software cost that made me decide that I should stick with PC. New copy of Capture One, new copy of Photoshop, all the little utilities such as Nero, etc, that don't cost a lot on their own, but soon add up, plus the much greater cost of the mac hardware, no thanks, I'm sticking with PC.
Dell factory outlet is here:
http://www1.euro.dell.com/content/pr...=uk&l=en&s=dfh