Diamond seemed to drop off the face of the earth yeara ago, they don't make cards at this time, that's why no drives. I am surprised your system is even fast enough to run XP if it uses a Diamond card.
You need to buy a different video card if your system can't run with the Generic driver included with XP.
I have some problems with my video cards, I have a diamond viper II.
when I installed windows XP, this OP doesn't seemm to be compatible with the video cards, I don't have much trouble, but some games (like fifa 2003 or need for speed II)don't work, my kids can't even opened them.
I didn't find drivers to update diamond viper II with windows xp.
I will be grateful if somebody can give me any information