Do I really need Norton set to update automatically? My computer has really slowed down. Wouldn't updating once a week manually when I don't need to be online be OK?

YES
Without updates your machine will be vunerable to the latest viruses and security threats.

What you need to do is some serious maintenance on your system.

Here's my usual C&P for cases like this:


When was the last time you did some serious maintenance on your system ?

System maintenance includes:
Defrag
FULL patching
Virus scanning
Spyware scanning
removal of rubish files

Defrag is an inbuilt function in XP.
Open My Computer > Right click C: > Tools Tab and its there.

To make sure everything is running fine run both anti virus and anti spyware apps in normal AND safe modes. (make sure that they are updated first ! ;)) (AVG (http://free.grisoft.com/doc/1) is good and free AV)
(A couple of good removal tools are Spybot (http://www.safer-networking.org/) and Adaware (http://www.lavasoftusa.com/software/adaware/))

ALso an on line virus and spyware scanner is Trend Housecall (http://housecall.trendmicro.com/)

Just a note: actively running two AV's on one machine can cause problems.
So if you are thinking about it make sure your current one is disabled first.
Same thing applies to online scanners as well.

Removal of junk files is easy with CCleaner (http://www.ccleaner.com) a free app that does exactly what

If all this fails then a repair install may be in order:

Here's (http://www.microsoft.com/windowsxp/using/helpandsupport/learnmore/tips/doug92.mspx) the official Micro$oft way of doing it,
and Here's (http://www.geekstogo.com/forum/index.php?showtopic=138) one with screen shots.

Basically this installs windows over the top of your current setup.
So you don't loose any information you already have.

This lot should resolve your issue.

While Curlyben is right everyday updates give you the most protection, I think its not necessary to run the update everyday. From my experience with Norton most of the daily updates are just small updates/patches to the programm itself which are most of the time fairly big. The Virus ugrade files are on average between 200kb and 2MB. If this is your privat computer and you have only files on their you don't trade with your office and can live without in a worst case scenario then their shouldn't be any problems with a once a week update or you just choose from the update the virus libaries like is said they are not to big and even on dail up shouldn't take more then 5min. I have nothing against Norton for Central Antivirus Software but privatly, I think it sucks. If you buy the newest release and have a 3 or 4 year old computer, it could happen that it slows down because Norton is so demanding. I am using on my privat PC the free Version of AVG Antivirus its less Resource demanding, give a fairly good protection and its free not $20 to update the virus libs every year.