I have similar problems with IGS from CADKEY. Circles are split into two half curves which are actually splines and partial arcs become splines. This may have something to do with the export settings. Check the Solidworks site to be sure the export parameters are set correctly for your source program.
I have to go in and delete the splines and replace them with tangent arcs. What a PITA!
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Hardie Johnson
"Most people don't know what they're doing, and a lot of them are really good at it." George Carlin