"... do I really need Nortons (or any other AV etc ) or is Windows Security just advising me thet I have security on my machine"
Yes, you need an anti-virus running on your PC. One and only one
No, you do not need Norton 360 installed. It has an anti-virus included in it, but you can get an anti-virus program that's as good or better for free:
These 2 won't hog your PC's system resources like all Norton products do.
Yes, Windows Security is there to just report the state of your anti-virus and firewall protection. It can also be used to turn off the Windows firewall. It doesn't provide any protection.
"I do Internet banking so want to be sure my computer is secure."
Any Internet site dealing with money had better have its own security. They use encription to prevent other people from seeing what you are doing. The status of the encription is usually shown by a little icon of a padlock in the lower-right corner of the browser window. At least, Internet Explorer and all Mozilla derivitive browsers (Netscape, Firefox, Opera, etc.) use this symbol. The padlock should be shown in its locked state when you are visiting these sites.