only ai (illustrator) files as cross-sections in spline modeller AFAIK. everything else should be greyed out (OS X version).  it's not necessary to learn, use nor own a copy of adobe illustrator to draw vector paths in carrara's spline modeller.  however, conversion of bmp files to vector shapes (filetype.ai)  is problematic IMVHO without considerable experience.  conversion of bmp files to eps files is elementary, but not very useful.