Well, my compatriots said there is no difference. But there is! :) ... Actually it depends on where one lives in Iran. Here in Fars Province (where I live), we pronounce them differently and we always wonder why Tehranians don't pronounce these letters correctly! :))) ... And we are not Turkish nor Arabs. We are Persian. :) ... Anyway, it doesn't matter if you pronounce these letters in a similar way as many Iranians do that, as well. But if you like to know the differences, I give you this hint: غ is somewhat similar to the sound of 'r' in French language. 'ق' is a little bit different.