From a more philosophical standpoint (since you specifically mentioned SP2). You shouldn't be online with it. SP3 is 'great' I'm sure, but it is an old and unsupported OS. So, IMO, if you are on that old of hardware where you can't upgrade to SP3, then skip SP2 or hell even SP1, just run straight XP or even 2k with sp4.
2kSP4 is going to be solid and very lightweight, and you can 3rd party firewalls and virus protection if you must be online.
Bottom line is, if you can't run XP SP3, that machine probably shouldn't be used online anymore. Its 2014, XP came out in 2001.