Have them send you dxf/dwg if they are 2D files. Or step/iges if they are 3D files.
No converters that I am aware of for TurboCAD.
I used to use TurboCAD Pro - excellent value.
It has a large range of formats it can export to - as Anna mentioned, 3D can be exported to step / iges / sat etc.
If its 2D try dxf or dwg,