Hi SD. Congrats on your new iBook.
Most people will tell you that there are no OS X viruses in the wild. Personally, therefore, I don't feel there's a need right now to be overly zealous when it comes to anti-virus scanning. But realistically, it's only a matter of time. It all depends on how concerned you are about it.
However, if you're sharing files with Windows users (such as Word documents that could contain macro viruses and such), then it might be a good idea to have some sort of anti-virus strategy. Since I fall into this category, I pay for an anti-virus option with my server, the advantage of which is that there's no AV software bogging down my system. You'd have to check to see if Telus offers such a service. Otherwise, you can always check out <a href="http://www.markallan.co.uk/clamXav/" target="_blank"> ClamXav</a>, which has the advantage of being free.
Whatever you do, stay away from Norton, unless you feel your machine's running too fast and want to slow it down.
Hope this helps.