I have to agree. There isn't much hope of rebuilding your present system.

I suggest looking through the system builder's guide over at Ars Technica to get an idea of what it takes to put together a budget build these days that will still be acceptable for gaming. http://arstechnica.com/guides/buyer/guide-200803.ars/2

You can subtract certain items from their total that you already have, like the monitor, keyboard and mouse, optical drive, maybe the hard drive if you want to reuse it.

Another possible path is to take one of the budget builds from Dell and soup it up with a better video card. But you have to be aware that the bottom of the line Dells do not have much extra oomph in the power supply, and may not be able to support a mid to top end card like an Nvidia 8800GT or ATI 3850.