I have a motherboard that came from HP xw3100. Part number is 323091-001. HP d530 has the exact same mobo, based on the part number.

Strangely, on HP's website xw3100's BIOS and drivers have not been updated since 2003 whereas d530 has more recent versions. So, can I use the BIOS and drivers for d530 on this?

Thanks.

If your Computer was manufactured in the Model run that you quote as "2003 era" then this is your BIOS driver. The difference between the two MoBo might not be that significant but if you really want check get a magnifying glass and check all the stripes on all the DIODES. One different colored line or different combination of the all the same colors but in a different sequence is an actual difference in manufacturing technique. Maybe you should use a microscope just in-case the difference is only that big.
I use a BIOS driver for my Gigabyte GA-8GE800 Pro MoBo that were last released in 2004. I update with these in-case my current drivers become corrupted eg. refresh to make new-like