OK, I can't follow the link, was it supposed to be:
http://www.ascendtech.us/dell-dimens...4delrd203.aspx
(I think this forum tries to stop new users from posting links so not surprised it went wrong).
That board seems to have a long x16 slot on it, is that missing from your machine?
230W is not very much for a P4 machine, so sometimes I think they make them with the x16 slot removed to make sure no-one plugs a big power hungry 150W card in, and then complaining the system doesn't boot.
So, thanks to the power supply you are looking at a bottom of the range graphics card I think. Unfortunately Dell sometimes use Dell specific power supplies so I can't even recommend a cheap power supply upgrade as I have no idea if it would work.
An AMD HD6450 card seems to use 31W, is available in low profile if you have to use a x1 to x16 adaptor, and gives you DirectX 11 support and a fair upgrade from Intel graphics.
If you want Nvidia, you will be looking at a GT210 which I have also seen listed as 31W (hope that site can be relied on but sounds about right). That is only DirectX 10, but I doubt you would see much difference.
The question remains of just how much performance you require. These low end cards really aren't very fast, but if you only want an update from the Intel graphics on your 945 chipset then it is a big step up.
If you are brave and have a steady hand, you can cut the end off the X1 motherboard slot and plug a X16 card in without using an adaptor.
http://blog.zorinaq.com/?e=53
May seem bonkers to have most of the pins not connected, but they are actually designed to work like that!
What games are you hoping to run?