Sunhund

Hi. I just bought myself a new SATA harddrive. So now ive got one SATA harddrive at 200gb(A) and another at 300gb(B). Anyway, yesterday i tried to setup a raid system but it ended up kinda bad. I had installed an OS on drive A (the "old" drive) and had around 150 gb of files that i wanted to keep on it. So i turned the computer off and plugged harddrive A(from normal SATA, or whatever you call it) and B to SATA RAID plugins. The computer only recognised the B harddrive in the bios, i couldnt format it or anything, the A one worked though. Then i tried to setup a raid system but when i did the computer asked me to insert a system disk (it probably couldnt run the OS). So i plugged both harddrives back to the normal SATA plugs and installed an OS on drive B in order to restore the partitions on drive A.
Can anyone help me "convert" to a raid system?
/thanx

edit: btw, i found some threads on this forum about the same problem ive got