At this point you've installed XP and applied Microsoft updates. You've got your virus scanner installed and working. Now it's time to get the software you use installed.
Get out your CDs and start installing stuff you want. This might take you quite a bit of time and certainly is no fun. It's also a good time to clean house and be more selective about what you need installed.
You may well be installing more software from Microsoft (Office is common). If you do, you must apply Microsoft fixes, just like for XP. Again there are plenty of security bugs for Word and OutLook (especially). Don't use these applications until you have applied the updates.
After instaling Office, you need to install updates from Microsoft. Microsoft provides new fixes regularly (the schedule varies). After your first install of Office you will have hundreds of fixes to install. After that there will be fewer.
Start by visiting the Microsoft web site at http://www.microsoft.com/ and click on Office Update on the left hand side.
Then click on Check for Updates and after a bit you'll either see something about "No critical updates available at this time" or something like that below inviting you to download and install some updates.
As with the updates for XP, these can be very large. The first time you'll be asked to approve a certificate from Microsoft. Unlike with the XP update process, Microsoft will probably insist you have your Office CD around. You didn't put it away, did you? You probably have to dig this CD out every time Office updates are applied.
You need to check these updates regularly. XP will not be checking for you, but rather you must remember to do this. Office products (especially Word and OutLook) are favorite applications that crackers try to trick. There's a long history of these applications failing and installing software that infects your machine, so be careful to regularly check for Office Updates.
Now after you've got your applications installed and the last of your first set of Microsoft Updates applied, you can try to restore the data you saved before and get your Email working. You now can have some reasonable confidence that your applications will work reasonably and not infect you.