It depends on how you set up your RAID controller (to use RAID or not). If you do not use the RAID capability, but just use it for extra IDE ports, then Bandersnatch is right - they will show up in Device Manager, but will not show up under My Computer until you have formatted the partitions you've created.
If you use the RAID capability, though, you will not see all the drives under My Computer in any circumstance. A stripe makes all drives involved in the stripe appear as a single drive to the OS. In a mirror, you will only see one drive, as the other one just holds the exact same data, and the RAID controller hides it from the OS. If you are spanning drives, then all the drives will appear as a single drive to the OS.
Make sense? Check your RAID card BIOS to set your RAID configuration. Whatever you have there will determine what Windows "sees" or doesn't see.
And welcome to Tech Forums.