Does anyone know how easy it is to use these in a typical D&D 3.x game? Does that stats and abilities follow the same rules that are in the SRD for the most part?
I have it; been a while...
I think mostly same rules; though some of the monsters are damage resistant and take damage from weird stuff like in Eberron. And there's a taint mechanic or something.
This book has dual stats for both d20 and L5R. That being said, the CRs for a lot of the critters feel WAY off and the stats are 3.0, not 3.5, so some tweaking will be involved. The aforementioned Taint mechanics are in Unearthed Arcana (or online at d20srd.org). Aside from those points, I do recommend this book, as the creatures are quite inventive and flavorful.