That's the best way to do it. What doesn't seem to be right if I may ask ? It's just my guess. Look, since MS advises SP1 to BE installed (but not sure if integrated as well), it may mean that SP3 is not fully cumulative pack, and may not include all updates, hotfixes, etc. What I did with that clean ISO was only integrated SP3, and installed it a MS Virtual PC, but I haven't put this instalation on a further tests.