Do people with such heavily outdated computer systems buy software for them?

Bargain computers can be had for a cost less then many software packages or a few games that are easily within the spec of 2ghz and a GeForce or Radeon - especially if you consider an upgrade route and cut out the cost of a new monitor.

This is something I have considered myself when chosing which performance level to target. Gamers with gamer systems buy games, but people that don't prioritize their computer systems enough to keep them reasonably up to date - do they want to spend money on software? I don't know myself, but I'm winging it a little to target people with at least a GeForce 3 and 2ghz considering the low cost of such a system.

Projecting myself, if I had a really old system and didn't have the resources to upgrade it I think I would stick with buying a heavily modded older game like Half Life, and do the rest in freeware/opensource. I wouldn't buy a game unless it had longstanding value through mods or it was in a value pack or some other gimick with other games for a trivially cheap price.

Also, I would factor in that if the game targetted too low a spec, and I had a nice system, I would not want to run it. I would want to play a game that used the hardware I valued enough to keep up to date. For example, when I got a DVD player, I would no longer rent video cassettes as I was put off by the quality of them.

So, in this line of thinking, I think it's safer to target an audience that values having a decent enough computer enough to keep it up to date, and I'm not too terribly interested in limiting a game enough to run on an Intel video card and 500mhz cpu type system. Current games like Doom 3 hardly run on a 2ghz/GeForce 3 system as it is - so you are not competing head to head with AAA titles, but at the same time not dipping too low to cut off the upper ends of the market which actually spend money. Counterpoints are more then welcome though.