Windows XP SP2
Service Pack 2 for XP has been released. It is will be a monster download from the Microsoft servers, and way too big for dial-up accounts to download in any reasonable amount of time. They will need to get the upgrade CD.
SP2 is a huge upgrade that it changes many parts of the operating system. Given that previous operating system upgrades from Microsoft have sometimes been quite problematic. I, and many others, recommend waiting a few weeks to see how the upgrades go.
To do this, you need to turn Automatic Updating off in XP. Gp to Control Panel/System. Click the Automatic Updates tab. There are three choices. 1) Notify me before downloading and notify me again before installing. 2) Download the updates automatically and notify me when they are ready to install. 3) Automatically dowload the updates and install them on the schedule I specify.
Choose option 1) or 2). Do not choose 3) as it will download and install without asking you and if this upgrade turns out to be problematic, then you may end up with an unstable (or worse) system.
So, wait on installing SP2. Let others test it for you. If, in a couple of weeks, the reports indicate all is ok with the upgrade, then you can install it.