I can only speak from my experience in answering your queries. I was looking at Dell but in the end went with Toshiba from PCW for the similar reasons - good spec and it was there to take away.
"any problems with the standard warranty at PC World?" - there should be none - it comes with a one year warranty and current consumer legislation is pretty good. If you do have a problem go to PCW with all relevant facts and you will hopefully find them helpful.
"whether the operating system disks are provided" - yes, in the form of a recovery disk as well as three other disks with various programs and utilities.
"and whether SP2 is loaded" - it was on the one I bought on Dec 27th.
This was for a friend but had it been for me, I would have gone for a centrino machine - lightweight with good battery life. Your final decision will depend on what you want - a desktop replacement or otherwise.