|Why did you replace the motherboard? Did you install an exact Dell replacement?|
"I also changed the hard drive connector"
What does that mean? What did you change & why?
"It will not show the drive in BIOS"
Probably because you "changed the hard drive connector"
"when I try to install the OS (windows Vista), it asks for the driver"
If the hard drive isn't detected by the BIOS, the OS can't be installed. Also, no driver is needed when installing Vista. It sounds like you entire problem has to do with you changing "the hard drive connector". We need clarification as to what exactly that means.