napclientprov.mof error during Windows XP install

First, I'm going to guess that you either tried to slipstream Windows XP SP3 onto your install CD, or you have an install CD that is supposed to contain service pack 3. This isn't a bad thing, but from what I've read, the problem is related to CD's slipstreamed with service pack 3. Anyway, on to the fix.

The good news is that at this point of the install, napclientprov.mof should already be installed on the machine. You can click on Browser, then navigate to C:\Windows\system32\WBEM. You should see the napclientprov.mof file there, which you can then select and click OK to get the installer to continue. I don't have much more of an explanation than that, but it solved the issue for me so I'd expect it to do the same for you.

If you don't know what slipstreaming is, it is when you package Windows updates on your install CD so you don't have to go through all the updates post-install. It can save a lot of time if you have multiple machines to install Windows on, and it's pretty easy to do using a free program called nLite. To read more about how to slipstream updates, check out one of my earlier posts here.