I am a security newbie. For the past coulple of days I have been getting heavy warnings that my system is being hacked using a backdoor/trojan horse. I would like to know how to close the ports and/or clean the trojans off of my system. I am being attacked (i think locally) by a 68.xx.xxx.67 & a 68.xx.xxx.163. Are these local IP's and if so, how can I stop the attacks?

I am currently running:
Windows 2k w/ norton internet security
Moosoft's The cleaner
Norton Antivirus software
Imesh P2P client (is this unsafe?)

I have direct cable/dsl connection to my computer, should I also configure a router and/or proxy settings, and if so how do I do that? Thank you for any help at all.