Not all Dell's are bad.
Their entry level (2400 and 3000) systems (previously 2350)'s do not have AGP. They have standard power supplies, and are not "overrated" (e.g. a 250 watt Dell is generally thought to be as good as a 300/350 from a generic provider)
Their 4600/4700 series (and the matching server versions: 400sc/420sc) have full 8x AGP slots.
Their 8300/8400 series have AGP (8300) and PCI Express (8400).
Unfortunately, most people buy the cheap entry level 2400 with Celeron 2.4 GHz (Northwood based) CPU and onboard Intel Video. These are very limited systems.
Buy a 4600, 4700, 400sc, 420sc, 8300,8400 and you have AGP or PCI express, enough expansion slots, powerful P4 Hyperthreaded CPU's, etc...
You can put new mobos into dell 8300/8400 cases. You can put smaller slot mobo's (3 slot) into the 2xxx, 3xxx and 4xxx series.