Basically you cannot import large STL 3D mesh files into solidworks because of the inadequacies and flaws of the native STL importer. If you are running 64 bit mode and have Scan To 3D available to you you can, however import 3D mesh files in the .OBJ format which has no size restrictions.
1. You should be using 64 bit Solidworks with an adequate amount of memory - Most likely 8G min as mesh files take up a lot of space.
2. Go to "Tools->Add In's. Check Active and On Startup for Scan to 3D
Convert STL 3d mesh files to OBJ 3d mesh files
3. Download and install the 64 bit edition of Meshlabs from http://meshlab.sourceforge.net/ We will be using this to convert mesh's from stl to .obj file format.
4. Start Meshlab
5. Repeat as needed for each STL file.
5a. "File->Import Mesh." Select an STL file. Click on Open.
5b. "File->Export Mesh As" Select the "Alias Wavefront Object (*.obj)" file type.
5c. "File->Close Project"
5d. "File->New Empty Project"
Import OBJ 3d mesh files into solidworks.
6. "File->Open". Select the "Mesh Files (...)" entry at the bottom of the file type list. This shows both .STL and .OBJ files.
7. Select the .obj 3d mesh file you just converted.
Setup the mesh for further processing.
8. Once loaded, Set all three base planes to "Show"
9. Change the HORRIBLE default lighting by "Apply Scene->Backdrop with Studio Fill" or "Plain White". This gets rid of the unbearable washed out default
10. "Tools->ScanTo3D->Mesh Prep Wizard",
a. Select the Mesh, Next, Select "Automatic" the first time only. This ROUGHLY aligns the mesh symmetrically to the 3 planes but it's going to be off some.
b. Now Select "Numeric Input" To tweak rotate and translate the model relative to the base planes to get it perfectly aligned the way you want it.
With the above completed, the rest of the tools work much better.