If you're an experienced web developer but don't have experience with Android or iOS then your best bet is PhoneGap.
PhoneGap can be found here:
Once the HTML application is written it's only a few short steps to wrap it in the individual projects required for the various platforms.
For iOS you will need access to an Apple computer with the XCode ide installed. For Android your best bet is probably Eclipse. This runs on Java and as such can be developed on Windows, Apple and other platforms.