<< you must have your drives on separate channels on your raid card and make sure proper OS drivers are installed >>
if that's true, then it must only apply to certain raid controllers. I use an abit-th7ii raid mobo (hpt370 raid controller) and have 2 x 40gb ibm 120gxp's on the same channel on the same cable and my scores are what they should be. I ran HD Tach on a single drive by itself, my 2 drives in raid 0 on the same cable, and also again on 2 seperate channels. here are my scores
single drive - max 30880kps, min 15903kps, avg 28447kps
raid 0 on same cable - max 72736kps, min 16905kps, avg 46309kps
raid 0 on different channels/ cables - max 73126kps, min 15903kps, avg 46854kps
so for only using 2 drives, the performance difference is negligible. but anyway, i definitely agree on making sure you use the proper drivers for the raid card. windows likes to install its own driver and yes it works, but you lose alot of performance over the manufacturer drivers. also, what size did you set your stripe size to? mine is set to 64k, and i noticed before you could only set it to 4k but you never said what you have it set to now.