I pulled up the pictures on the Dell website. It looks like a standard micro ATX MB layout. The rear panel connector does have a removable pop-out. The only problem area may be the exhaust fan shroud from the CPU cooler to the rear of the case. You may have to leave that off with a new MB.
http://www1.us.dell.com/content/pro...00?c=us&cs=28&l=en&s=dfb&~tab=viewstab#tabtop
Now the risk issues:
-The copy of XP home you are using may be rigged (liscenced) to only work on a Dell brand MB. If that is the case you have to buy a new copy of XP.
-The power supply may be too small to add a serious vdieo card (I assume you want gaming capabilities). Pull it out and find the label. Post the power rating (300W, 350W, 400W, etc) and the current ratings for the +3.3V, +5V and +12V and any limitations mentioned like "combined 3.3V and 5V load should not exceed 180W" adn we can tell you what it will support.
-Case cooling may not be good enough if you add a hefty video card. What cards are you considering?
Aside from all that there is a procedure for swapping MBs. Sometimes it works sometimes you are forced to do a clean install. Basically you go into Device Manager and uninsatll all of the devices (video, audio and system). Then install the new MB and boot up.
If you try to install a new MB make sure you physically have ALL of the setup, driver and XP CD's for that Dell. They often put the repair or install data on a seperate partition on the HD. If you trash the new MB install and decide to give up and go back to the Dell MB you will need everything in CD form.
Any chance you can just order a new MB from Dell with a video card slot? It will be more expensive than buying one off the shelf but will avoid some of the technical risks above.