Is there a way to use free software to convert SMILES strings to structures?
According to the website, Open Babel should do the trick: Documentation - SMILES, Sourceforge.

For example, the following code will give you a neat SVG file of the molecule benzene:

obabel -:"c1ccccc1" -O benzen.svg


If you experience problems using it, you are welcome to ask more specifically.

Alternatively, you can use a web-query from the national cancer institute. It is easily accessible by the following code

http://cactus.nci.nih.gov/chemical/structure/"structure identifier"/"representation"


For example: benzene, "structure identifier"=c1ccccc1, "representation"=image.

Another open source solution, where you can directly export the structure into a molecular editor is Avogadro. (It uses Open Babel though.)

Depending on the actual problem, however, there might already be more advanced routines.