...Or you could just install SP3 without agreeing to the supplementary EULA. How do you do that? We're glad you asked. Ordinarily we try not to get to close to encouraging or helping people to crack software, but we think this case is a tad different. As we said earlier, SP3 is to a great extent an exercise in fixing bugs in something you have already bought, and it is an outrageous imposition (OK, we didn't say that earlier) for Microsoft to seize more rights for itself as a condition of those fixes being applied.
A helpful tipster directed us to a cute product called Enabler, which you will find
here. Enabler is one of a number of handy things on this worthy site, and seems to do quite a number of handy things itself. But what it does that's important from the point of view of people wanting to install SP3 is allow you to click OK after you've checked "I do not agree" to the supplemental EULA. Note that you use it at your own risk, don't blame us if, etc (insert draconian Register EULA here).
This, seeing you're in too much of a hurry to read the instructions, is how you do it. Run Enabler, then start the SP3 install. Click on "I don't agree" when you get there. The OK box is grey, right? OK, go to Enabler, and scroll down until you get to the entry for Windows 2000 Service Pack 3 Setup Wizard. Double click on it, expand the tree then go to the entry that says &Next> (Button). Right click on this, and click on Enable. Now return to the SP3 Wizard, and you'll magically find you can click on Next even though I do not agree is checked.
Wonderful, isn't it? And as far as we can figure out you're not doing anything wrong either. Well, not much. It does say above the supplementary EULA that to continue with setup, "you must accept the agreement." So Microsoft's lawyers could argue that you're not licensed to use SP3 because you haven't agreed. Which is approximately the same territory as the wording in the WinXP EULA which says you're not licensed if you don't activate it in the approved way (so you could have paid for the product, but by using a workaround for product activation you'd be invalidating your licence anyway).
Microsoft's lawyers are not going to come after you for warezing a service pack, and we doubt very much they'd come after you for installing a copy of WinXP without agreeing the licence (NB we don't know if Enabler would allow you to do this, and we're not about to reinstall XP again today just to find out). So you're probably in the clear anyway?
Well, not exactly, because if you've installed a Microsoft product without agreeing to Microsoft helping itself to data from your machine, then legally speaking it's your move. You may be in breach of your licence agreement, but Microsoft will be helping itself to this information anyway despite your not having given it permission to do so. So you're going to have to sue. Good luck.