Thunderbird for mail, and I'm going to break the mould and suggest Opera for browsing. Just not if you want to edit S2 layers, since LJ has decided not to support Opera anymore. It has many of the features built in as standard that you have to add to Firefox with plugins, and it still loads faster for me than a relatively bare bones Firefox. It has a session saver as default, which is wonderful if the program or your computer crashes, or if you accidentally close it and lose all the many tabs you had open. I don't remember the other reasons I ruled out Firefox due to too many nifty Opera features, but you can probably get a lot of them in plugin form for Firefox. A lot of it is probably preference. I say try them both :)

I don't know much of anything else, except I'd say XP Pro and Norton make a decent combination. Check how long your license is for - my computer came with 3 months of Norton, then I had to either buy a license or get something else (since my university provides free Sophos and Ben's university provides free McAfee, I went with the latter option).