Vista - Can't get laptop to update to SP1

Have Dell XPS laptop running Vista Home Premium 32bit, purchased approx 18mths ago. Had to restore back to factory delivery state from a recovery drive copy. VISTA is updating tons of updates but won't offer SP1 for update. I cannot install key software until it does!

I notice that it failes to install KB943055, but when I try to manually install I am told this update does not apply to my version of VISTA. May or may not be relevant.

SP1 does not appear in the update history list, and is not shown on winver or control panel/system as confirmation. Windows update informs me I have no updates outstanding!

How do I get my system to install SP1 & SP2 from here?

Please - any assistance would be greatfully appreciated.

Well before anyone was able to post a reply - I made a second attempt, reinstating the Dell factory delivery state, again letting update install all available updates, then manually installing SP1. This time it worked for some reason, and only took 20mins, not the expected 2 hours!

So now I have to look at installing SP2. Was just informed on another thread that I only needed to install SP2 as that included everything in SP1. Wish I knew that before - I was under the impression I needed to install SP1 first.