How to bundle dylibs correctly on OSX?

My app depends on libcurl and libexpat. I have no specific requirements in my app and want to target 10.6.0 and up. At the moment I just link to the libs the standard way ( added them with Xcode ). But that messes up my app. If I compile it on Lion it won't work on Snow Leopard. It complains the libs are to old. How do I spe开发者_Go百科cify a minimum version needed? Or should I just copy the libs into my bundle? Can I copy the ones from Lion to make it work on 10.6? Thanks

Edit: Is this as easy as setting the Base SDK to 10.6?

Its as simple as using an older base SDK. In this case 10.5