mine is a 307 diesel (2 litre) estate
costs around 450 a month (fuel inc) once the taxman robs you blind. I was doing 700 miles a week (at least) but am now doing less than 70. the car was worth it with high milage, but not with anything else. you need to be doing around 34,000 pa to make it viable really.
there are some ECO schemes that are worth looking at, provecta are a prime example and this will save you money yet give you company car benefits :- fuel card, service, maintenence, breakdown, road tax, insurance, etc.
best bet is to ask your employer what the cash alternative to a company car is and do the sums.