Speedjeans - I don't know what to say. Not to take antimalarial prophylaxis in Tanzania is tantamount to suicide. Not to take antimalarial prophylaxis in ANY malarious area in EXTREMELY dangerous.
Cerebral malaria can kill you dead dead in less than 48 hours - other forms may take a day or two longer. Even after treatment, malaria sporozooites can hang around for years and cause relapses.
Make no mistake, malaria is an EXTREMELY dangerous disease - take it lightly at your peril.
Different countries and different areas harbour different strains of parasite which require different antimalarial propylaxis - find out what you should be taking from your local big hospital or tropical diseases institute (Or phone the London School of Tropical Medicine and Hygiene) - most GPs don't have up to date info. Start prophylaxis well before you go to a malarious area and continue for a few weeks afterwards. Mosquito repellents and fans are not enough. You need a mosquito net for sleeping and long sleeves and long trousers in the evenings.
FYWH - AIDS may now a numerically bigger killer, so what? Malaria IS largely preventable and can kill you stone dead within days. Antimalarials (particularly Lariam) sometimes make sensitive people feel peculiar and some MAY have long term side effects (tho' these are rarely serious/lethal. Take 'em and live.
People get infected abroad and come home to Europe - they then get sick, but by the time the local hospital has gotten round to diagnosing something as "exotic" as malaria and treating it they are often too far gone and die.
As zippyz says "Trust me.. you DONT WANT MALARIA"