simple modelling

i''m trying to create a rounded tetrahedron (a triangular based pyramid with rounded edges), is there a simple way of doing this? - i''ve looked at using motion blur & antialiasing to give the impression of roundedness, but its sooooo slow... i could work out the maths, but i''d rather someone else have done it already! - or is there a (free) modelling package which will let me do this easily? thanks alistair