Well, unfortunatley no, considering its technically impossible to uninstall. You might be able to MANUALLY delete all of the files for it, "If" you knew where they were, and you might delete all the registry keys, but as far as I know, you cant really "Accidentally" uninstall DX8.
Did you ever consider the possiblity that you DO have it, and something else is causing your problems?
go to "Start" then "Run" and type in "dxdiag" and hit enter, this will tell you what version of DX you have, and will test all of its components. Make sure your using 3dmark 2001SE earlier versions prolly wont work on XP.
i did that before and it says -- DierctX Version: Not Found anyway when i try to reinstall it, it just doesnt seem to work it goes way to fast. I mean i click install and it instantly says Installaition Complete so idk how to get it back on. I heard that I might need to download Service Pack 1, but im on a 56k and we aren't getting cable for another month or so and none of my DX games work now.