Unable to Install XP SP2, Don't Have Permission

I was trying to install Service Pack 2 on an older PC running Windows XP and it won't let me.

I get the message "You do not have permission to update Windows XP. See your computer administrator."

But I am on the Administrator account, and according to the Users applet in the control panel, it has all the administrator privileges.

Are there some registry hacks or other workarounds for this?

Why are you trying to install SP2? SP3 is out now and covers all the updates from SP1.

You really should install SP3 and forget about SP2.

Is your XP a legit version?

I read somewhere that SP2 has to be installed before SP3.

Nope, that's never been the case with Windows Service Packs, all you need is the latest one.

You need to have at least SP1a in order to go to SP3. What is the current SP level?

http://support.microsoft.com/kb/322389/