Older versions of XP need the driver on diskette, so the install program will read it after you told it by pressing f6 when it ask for scsi drivers. That's a well known procedure.
Did you already ask Dell customer support, or look at their site? Of course, it's possble they don't support it. Then it might be a nice question for our new Dell forum!
I've ordered a dell optiplex gx 755 without OS (cos i dint want to have vista as OS)... now when I'm trying to install xp its not detecting the hdd now... may b coz its SATA n win xp doesn't knw anythn abt SATA... I've read in a few forums on how to slipstream the sata drivers with xp.. but howeva m unable to find the sata drivers for dell optiplex gx 755... where can i download the sata drivers for dell optiplex gx 755??? Pls help.