Go to Midway's web sight and get one of these:
GrovTec Sling Swivel Stud Adapter AR Forearm Steel Black.
If your factory fore end has the holes in the bottom, then this will work for the Harris style bipods (which aren't all that bad depending on the manufacturer). Other than that, plan on spending around $200++ for something like a GG&G or Atlas 'top shelf' bipods. If you want a rail mounted (Picatiny) bipod, you can 'fabricate' something like a MagPul rail mount section (probably like a 4-5 section rail - polymer or metal) on the bottom of the factory fore end.
This is a GG&G XDS-2 bipod mounted on my DDM4 carbine. It pans 20 degrees L/R, and, cants 25 degrees L/R of center. The bipod legs will also lock forward 45 degrees. It's attached on a M-Lok Picatiny rail section.