That would be hte 4go then, I upgraded to that identical card when I had my Inspiron 8100. Let me take a look and see what upgrades are available to you, you should have 2-3 different options.
Okay the best I was able to find is a Radeon Mobility 9000, basically this is somewhere between a geforce 3 and geforce 4ti. I t does add hardware direct x8 so it can paly newer games and it's faster than what you've got, but it's not going to be a huge jump. Here's a link to the card and a (spendy) place you can buy it new:
They also make a quadro card, (roughly a geforce 4 4200 ti) but they're difficult and hard to find.
I would recommend taking the part number from this site and searching pricegrabber and ebay (i bought my upgrade via ebay), I think this runs somewhere between $100-150.
For instructions on how to install go here:
or check the Dell service manual (available on their site). ATI should have the specific notebok drivers for this card.
This page also lists the compatibility with certain laptop lcds, you'll want to find out what they do and don't work with and what you've got. To fidn out what you have I'd ask the folks over at the Dell Support Forums, they are generally very helpful in this situation. This forum is on Dell's website