I'm running 2k pro and captured a lot of room by deleting my DrWtsn dump file - about 45MB. Just search for "*.log" and you'll find it. Also kill FindFast. Get rid of all the user-created files you don't need. You didn't say how many or what size your partitions are. Set up your apps (Word, WP, Excell, QuatroPro, etc) to save by default onto a partition other than the one your OS is on. Also set Outlook Express, if you're using it, to put its folders on the same partion with Word et al. Try to get everything off your OS partition that doesn't absolutely have to be there. There are also some swap file things you can do but I'm not knowledgeable enough in that area to help you there. Get everything off your desktop, even wall paper, they use memory. Minimize apps when not in use, uses less memory. Listen to your HDD for a lot activity. If you hear a lot of "buzzing" then you are having memory problems.
Then scandisk followed by defrag (as previously suggested). Defrag once/month. Use DiskLite if you don't have another built-in defrager. And I would get rid of all the norton stuff except NAV. You don't really need a lot of stuff to clean up your system. StartUp Cop, Startup Control Panel, RegCleaner, and maybe a few others will be all you need; and maybe not them.
Sorry for the disorganized order of my suggs.