There is no direct option to save and open files to lower version.
So this is not possible.
If you want to open drawings in lower version then there is a work around:
You may save your drawings to DXF format and this may be opened in SolidWorks 2007 but remember these are set of lines only there will be no relations & reference with your 3D parts & assemblies.
If you want to open 3D models in SWX2007 then you may save your parts & Assemblies in .STEP or .IGES file format. These parts may be used in Solidworks 2007 but again it will not be referenced with original parts.
Just one point on the saving of a 3d model to a neutral format, generally teh preferred format is parasolid if it is going to be opened by another solidworks user as that is the native format of solidworks, less of a conversion process and less import problems usually
Just make sure you save in a version of Parasolid that SW2007 can read.