Where I can found a free download for a converter SW to STEP format? (Excuse my english, I don´t like use the google translator)

Not sure if these are free:

http://www.datakit.com/en/cross_manager.php
http://www.datakit.com/en/crosscad_pro.php

What formats?
SolidWorks files use the Microsoft Structured Storage file format. This means that there are various files embedded within each SLDDRW (drawing files), SLDPRT (part files), SLDASM (assembly files) file, including preview bitmaps and metadata sub-files. Various third-party tools (see COM Structured storage) can be used to extract these sub-files, although the subfiles in many cases use proprietary binary file formats.

Solidworks 2010 SP3.1 opens/saves following file formats:

* SolidWorks Files (*.sldprt, *.sldasm, *.slddrw),
* Part Files (*.prt, *.sldprt),
* Assembly Files (*.asm, *.sldasm),
* Drawing Files (*.drw, *.slddrw),
* DXF (*.dxf), DWG (*.dwg),
* Adobe Photoshop Files (*.psd),
* Adobe Illustrator Files (*.ai),
* Lib Feat Part (*.lfp, *sldlfp),
* Template (*.prtdot, *.asmdot, *.drwdot),
* Parasolid (*.x_t, *.x_b, *.smt_txt, *xmt_bin),
* Stereolithographic STL (*.stl)
* IGES (*.igs, *.iges),
* STEP AP203/214 (*.step, *.stp),
* ACIS (*.sat), VDAFS (*.vda),
* VRML (*.wrl)
* Catia Graphics (*.cgr),
* ProEngineer Part (*.prt, *.prt.*, *.xpr),
* ProEngineer Assembly (*.asm, *.asm.*, *.xas),
* UGII (*.prt),
* Autodesk Inventor Part (*.ipt),
* Autodesk Assembly (*.iam),
* Solid Edge Part (*.par, *.psm),
* Solid Edge Assembly (*.asm),
* CADKEY (*.prt, *.ckd),
* Add-ins (*.dll),
* IDF (*.emn, *.brd, *.bdf, *idb).

A TransMagic plug-in for SolidWorks is available that expands its import/export capability via native CAD kernels

What CAD software are you using? Some software, has import features. If it's a SW model posted on here, most people will upload a Step/Iges file if you ask. Also, try Google, SW CAD conversion, sld.prt to step or Iges, dxf, etc.