If theyre exactly the same models of drive, you can get away with swapping the boards over (provided you can release any ribbon cables without damage).
If it's a power issue / controler board issue the local office of the manfacturer (western digital, seagate or whover) may offer assistance for a smaller fee.
If you can get the drive to spin up, and can copy the data off it then thats fine. If the data is damaged then Spinrite should be able to rescue the vast majority of it (if not all)
http://www.grc.com/spinrite.htm Dropping the guys at GRC may also get you some help incase there is a known issue (and workaround) with the drive that is causing you problems.
If it's a head crash or one of the platters screwing up it's more than 500 $ Aus the last quote I got for a drive recovery was 1400 UKP for a 20 gig drive (and you don't want to think about the price for getting a tape recovered).
Meanwhile make sure the rest of your porn collection backed up, as I beleive certain members of the forum here may be able to assist you in that ;)
Rob...