how long do i need left on my passport to travel to south africa?

i'm going to south africa in january 2009 for 14 days and my (british) passport runs out in april2009

6 months, so you'll need to renew it before you travel.

Not the question you asked, but when you get a new passport you will avoid a pitfall that plagues international visitors to South Africa: blank visa pages. South Africa has been known to return travelers who don't have two blank visa pages in their passports! It's an odd little rule, but can cost thousands of dollars if you're not careful.

The link below is on a USA site, but the rule applies to all visitors.