I really want you to understand that upgrading your video card also means you will probably need to upgrade the power supply. However, since you are using a Dell, it will be very difficult if impossible to find a power supply that will fit your case. Dell is well known for that and have seen many techs say the same thing.
Can you look on your power supply and see what the wattage is? The card that was mentioned in this post requires at least a 450 Watt Power Supply, not to mention the power supply is recommended to have a 2x4 power connector to plug onto the card.
With that said, check out this link given by a pinned topic in the "Games Forum" here. It lists the best cards that are out every month, and the best for the money.AGP Cards
This is about a year old, but you have to remember, AGP is very dated technology.
And the Introduction Here
Edit: And by the way, I believe your motherboard can support 2x/4x AGP. Anything that has the 4x should work. Even if it says 4x/8x.
Edited by Ferrari, 21 March 2009 - 07:28 PM.