Is there a conversion file to import a SW 2007 file into the SW 2005 version?
Nope, only thing you can do is save as neutral format (IGES, STEP, X_T etc.) and open that in SW 2005. This will only give you dumb models and assemblies that "float" (no mates) and drawings are not an option. If your files must go back parametric to SW 2005, talk to folks at http://www.elysiuminc.com/ Maybe they can help you for a fee. Good Luck.
I recommend saving as parasolid in 2007, then opening that up in 2005 and using FeatureWorks to recreate the features. Start with superfacial features like fillets and drafts, then work your way to the base features. This is the only way to have a functional model moved back from a "future version". Matt http://sw.fcsuper.com