You should never have two antivirus programs (or two firewalls) running on your computer simultaneously, as this can lead to serious system conflicts.
There are two security suites which are generally reviled by the majority of the 'regulars' here in AB's Technology section. The first is Norton. The second is McAfee. Both will do the jobs required of them but (because they're both 'resource hungry') only at the cost of slowing down your PC (and at unnecessary expense to your wallet).
Most people around here would suggest that you should ditch Norton as soon as possible. You can't uninstall it in the conventional way; you need this special tool:
http://service1.symantec.com/Support/tsgeninfo .nsf/docid/2005033108162039
Then, if you insist on paying out good money for security software, the most popular full commercial product (among those who do a bit of research, rather than using whatever happens to come with their computer) is probably Kaspersky.
However, most of us don't spend any money on security software. We simply install the three essential elements (entirely free of charge) separately. The means using either AVG Free Edition or Avast! for ant-virus protection, Zone Alarm Free or Comodo as your firewall and as many 'run on demand' anti-spyware programs as you like (such as the free versions of AdAware or SpyBot Search & Destroy).
Most Flash-based sites will run perfectly happily under older versions of Flash player. However, as long as you don't experience any problems with the installation (which occasionally happens) I can't think of any reason why you shouldn't upgrade to version 10.
Chris