I've installed SP3 on a "XP" machine that didn't have SP1 or SP2. I wonder if you meant it was forcing the udpates to IE 6 and such in order to allow SP3?
In any case just take it online and then use Windows Update.
I have an old computer with XP that has never had the service packs installed. I tried to download SP 3, but cannot install until I have SP 1 or SP 2. I searched for these, but the official websites say neither is available. I am hesitant to try elsewhere. Is there some safe way to download these older SP?