SP3 adds a DMCA-comliance restriction on CD and DVD drives, to prevent sharing of copyrighted CDs and DVDs across many computers. If you have a computer without a CD/DVD drive, you are out of luck. I've tried looking for something that shares the drive proper, even a special driver-hack, like what makes flash drives partitionable, but no. All network access to CD/DVD/BluRay drives is locked out since XP SP3.

Microsoft had to do it so they won't get lawsuits from the RIAA and MPAA to this concern.

There may be a way to share the drive, by downgrading to XP SP1, but the lockout could also be on the client computer. Meaning the computer being used to access the network CD ROM drive has to have XP SP1, as well.