Making xp legit.

A business down the street hired me the other day to do all of their computer work because the guy before me messed a lot of things up and apparently did nothing right.(Half the office is on their domain, the other half is on the workgroup, all the software seems to be illegal, etc.) Well almost all of these office computers have the wga thing on them. I told the lady that runs the office that she needs to make all of these computers legal. Well I know you can get the discounted serials if you mail them a copy of the "forged" cd you purchased from someone, but there isn't one in the office to be found since the guy that was previously doing their computer work installed the same illegal copy on all the computers.
So I just told the lady to purchase a few 3-packs of xp pro, sp2 oem since there's only like 6 or 8 compies in the office.
Am I correct in thinking an oem key goes with an oem disc/install?
My question is after the lady purchases the licenses, how do I switch the serials over to the new ones? The existing ones aren't oem versions(obviously) so deactivating windows and reactivating with a new key won't work right?
I've never had a problem with my windows installs not being legit so I don't really know how to go about making these ones legal without reinstalling.

I don't recall off the top of my head; business environs are typically excluded from activation (what a PITA it would be if we had to activate at $WORK). OEM keys will work only with OEM disks and OEM installs.

The guy who was doing their computer work beforehand should have his nuts busted.

I believe that You can also call Microsoft and purchase the proper materials and CD Keys from them under a business package deal. As long as they have the proper license and/Or number of CD Keys, they should be OK after that.

Jellybean Keyfinder can be used to change the serial on a current install.

However, depending what else is on the machines you might be better off slipstreaming SP2 onto a disk and making an unattented install disk, and starting from scratch.

But back-up everthing that's important like business files etc wouldn't want to loose any of it just incase something goes wrong. The first guy who did it must be a dodgy teckie it's shame if she paid him and he's done all that.

But I think a complete re-install would be best you never what rubbish that last guy put on there.

What kind of PCs are these? Most businesses I know just buy like Dells or something. They come wth XP preinstalled, and a COA on the case, but often no CD.

If the install is an illegal one the best thing is a full format and fresh install. Who knows what kind of junk was installed when you use illegal softwre? Also you mentioned that the network was never setup properly in the first place. This is a perfect opportunity to come in and clean everything up.

I would also check the server to make sure that it is running a legal copy of WIndows Server while you are at it.