Service pack two did wonders for my constantly crashing system... so did removing nortan but that's a different story.

Service pack 2 does have alot of bug and security loopholes fixed, but bear in mind there are some minor alterations (you probably won't notice) such as a further restriction on the number of open connections to 10.

There are a few more that will probably remain invisible to most users... but if you do notice any differences, be sure to have a google