The Oxford Roland (from Oxford, Bodleian MS Digby 23, the oldest ms) is of course digitized :P but you can find a transcribed older edition at the Bibliotheca Augustana.

Pretty much any vernacular from the mid-12C, you're talking substantial differences with the modern language. One thing I find is that thanks to differences in dialect, any text gets easier as it goes along. If you wanted, you could pick up an Old French grammar book to get a sense of grammar morphology, or you could just rock and roll with an online Anglo-Norman dictionary and a translation aid.