We are presently using our 17" CRT monitor and would like to upgrade to a 22"-24" widescreen LCD monitor. What is a good choice in the $300-$500 range?
I would also like to get a graphics card in the coming month to upgrade the system. Presently the system is using the onboard graphics on the motherboard which is obviously not ideal. I am looking for a card in the $180-$300 range.
On the low-end of your proposed budget, a 22" LCD has a 1680x1050 resolution and the cheapest video cards worth buying for it are the ATi 4850 or the Nvidia 9800gtx+.
Moving up to the mid-high level of your budget is a 24" LCD that has a res of 1920x1200 (more than 1080p). It also requires a more powerful graphics card to get playable framerates with new games. The lowest I would go here is the ATi 4870 1gb or Nvidia gtx260 core 216.
My preference is to the Nvidia cards as they perform better and have more driver updates (probably why they perform better). The only killer card ATi has is the $450+ 4870x2, and Nvidia will release a gtx295 soon to compete with it.
More bad news though is that your Dell PSU will not power any of these cards reliably. I'm in the US, and a 550w Corsair that could power any of these cards is only $70, so I suggest you look around. Make sure the +12v on the PSU has at least 35amps.
Another gremlin is that (I'm almost certain) none of these cards will fit in the Dell case, except maybe the 4850 which is the slowest card of them all.
Honestly, if you want to play some games...take back or sell the Dell and build a PC. For what you payed for the Dell and your budgets for the new monitor and video card, you could have built a really nice system with no shortfalls like the Dell has (power supply, case size, locked BIOS = no overclocking...yet Intel chips are made for overclocking, etc.).