What raid card are you useing and its chipset?
Most likely with kernel 2.6 you will just set it up as jbod and the make software raid.
According to docs;
VIA 8237 Software WORKING
Promise PDC202xx/PDC203xx Software WORKING
Silicon Image 3112[a],3512,3114 Software WORKING
Promise SX4000 (PDC20621) Hardware WORKING
3Ware Escalade 7xxx and 8xxx Hardware WORKING
Gentoo forums most likely have had this discussion and how tos...maybe here...try a search.