You need an AGP video card.

Technical Specifications: Dell Dimension 4100 System Reference
http://support.jp.dell.com/docs/systems/dzuul/specs.htm#video

One 4x AGP slot.

http://support.jp.dell.com/docs/systems/dzuul/specs.htm (see expansion bus
section)

Just go to dell.com and search.  That's all I did. :-)

See;   http://support.dell.com/support/edocs/systems/dzuul/specs.htm

Why do you think you need a new video card?

Are you trying to replace the existing video card, or to add a second one?

Bill -- (Remove KILLSPAM from my address to use it)

Open up the computer (you will have to do this to put in a new card, anyway).
Look at the slot that the video card is plugged into.  If it is different than
the 3,4 or 5 next to it, it is an AGP (there is only one AGP, but usually more
PCI slots).  The AGP slot is also spaced further away from the back panel of
the computer, and is brown, and the PCI ones are black or white.
If you currently have a PCI card, but there is an AGP slot available, you
could change to an AGP card, or vice-versa.  Most newer cards are AGP, except
some very new ones, which now are PCI-E (which you don't have in a Pentium 3).

|how do i find out if i have a pci or agp slot.  I need a new video card and
|don't know the one to buy.  I'm running a dell dimension 4100 with a pentium
|3 with windows xp