|Are you behind a router and did you install a firewall before going on the net. You may be picking up something right away that has nothing to do with WinXP.|
You don't need to install SP2 then SP3. SP3 contains ALL the updates from the begining until the release of SP3.
I suggest you download the distributable version of SP3 and burn it to CDR. Then re-install Windows, drivers, SP3, etc while you are NOT connected to the internet at all. Don't even plug in the NIC cable.
Then if you still have problems with the service packs then you will know for sure it is them.
Are you re-installing using Dell restore disks? Below is a link to download the redistributable version of SP3.