newbie Qs: nr of elements

newbie

I'd like to do some calculations on drag and lift of airfoils in incompressible viscous 2D flow wit re nr around 10000 to 100000. my question is, what is considered a large enough number of elements and also how big should the calculation area be ?

I've done some tests using femlab and using a 3GHz machine with 512Mb memory it allows around 20000 elements without a turbulence model and maybe 10000 with the k-eps model.

would using another software (openfoam or similar) allow me to use significantly more elements ?