We just lost a hard drive at work, and are running Win XP. When we install a new HD do we have to re-register XP?

Do you have a backup image to restore to the new drive? If so, and all the rest of the hardware is the same, then probabaly not. Did you have XP home or pro? Was the partition encrypted?

Unfortunately we don't have anyway to get the data off of the old drive. This will necessitate a fresh install on a new HD. Is there going to be a problem with MS on this front? It is XP Pro (work net).

You will need to reactivate it, but there shouldn't be any problems with that. The most complex issue that I ever had with MS was transferring one XP license from one machine to another, and that was handled with no problems.

you wont have to reactivate for just a hard drive. Xp activation is supposed to kick in when 6 hardware devices change, or, 4 devices if one is a nic. (They love them mac addresses.)

Yes, but if you have to reinstall, you're given 30 days to activate again.

after listening to all this garbage its really nice to know i'm not allowed to take my engine out of one car and put it in another without a bunch of headache. F#@K MS. If i want to put a pontiac engine in my cutlass then damn!t i'm gonna do it.

OK, calmed down?
Right, firstly it is totally upto MS what they allow you to do with their product.
It is part of the license agreement that you agreed to when you installed their OS.
Secondly, you DO NOT own Windows.
You have purchased a single license to run it on a single PC - your "engine" argument is not comparible, unless your Pontiac came with a license to use the engine in a single vehicle only.
Thirdly, MS are not stopping you MOVING your OS between computers, however as stated above you have purchased a single license to use on a single PC - remove it from your old PC and install it on your new one, transfer of license and job is done.
In the unlikely event the online activation doesn't work a five minute call will solve the problem.

Don't like this?
Think this is too much of a headache?
Then don't use an MS OS - it really is nice and simple I'm sure "anybody" can cope with it.