Re: 5700 or 9100
Quite simply, the 3000 model doesn't come with an AGP slot. I suppose it keeps costs down and that's why it's a budget PC. If you're fast and can catch a good sale, you can grab one of these (celeron 2.4GHz, 256MB DDR RAM, Win XP) for about $300 CDN which comes to about $200USD.
It's a really good deal if you can live with the limited upgrade options.