Yes Norton is a major cause of a sluggish start up, but with your specs it should eat it up, run MSCONFIG and see what's in the start up as that time for a start up with those specs is a joke.
I recently built an AMD 2500+ Barton on a ASUS A7V8X-X running FSB 166MHZ 333ddr with 512MB PC2700 crucial RAM for my mother inlaw and it is running NIS2004 + System works2004 and all the usual MSM messenger and the rest, and it is ready in about 10 seconds after the welcome screen so it's defintaly not your specs mate.
Your IDE cable and integrity of your hard disk. For the hard disk use click here Do a control alt delete and check any processes that are using a disproportionate amount of processing power. You may want to start your pc with the minumum number of processes running to see if the problem is software related. Also try taking your case off to check that your CPU cooler is working properly. You are quite correct in setting the cpu fsb at 166.