What lens would be good for the Olympus E300 DSLR? For portraits?

I am confused on what lens to buy. I only have minimal expierence with SLRs in the first place.

I have a Olympus E-300 Digital SLR and I was wondering what lens I should buy? I am going to be taking potraits, so what lens what be more benefical for what I'm going to be using the camera for?

Thanks

Here are some free online lessons using the Olympus E300:
http://olympusdigitalschool.com/e-system...
For this lesson on 'Portraits' - http://olympusdigitalschool.com/e-system... - the lens that was used is the Olympus 14-45mm f/3.5-5.6 Digital Zuiko Zoom Lens.