It's now been pushed back again to June 2, 2009. They keep on pushing it back. It better be really good, been waiting for this game for such a long time. If you want to know more about it, here's the website for Undisputed.
http://www.ufcundisputed.com/#/features
Its also listed on Gamestop:
http://www.gamestop.com/Catalog/ProductDetails.aspx?product_id=71805