I am new to developing on android so be gentle

I am having an issue when I create new projects in eclipse, when ever I create a new project the R.java file is not always being generated, in some cases the src folder is not generated.
I have tried using clean and build, refresh, dont autobuild etc etc and sometimes I can get it to generate the file and recognise it but a lot of the time it still ignores it
From the title as well I am developing using eclipse for Mac just incase that is going to have any bearing

Any thoughts would be really helpful
Thanks in advance
Ben