^I'll add a few more that come to mind, in order of steps to follow with most common errors people seem to make:
RAID not enabled in the BIOS- You have to enable the RAID controller to get the RAID BIOS screen to show up during POST, with the option to enter the RAID BIOS (which is seperate and different than the regular BIOS)
RAID not setup correctly in the RAID BIOS....During POST does the RAID controller appear and show the 2 drives as a "Striped Set" or "RAID set 0" or something like that, with 300gb of space? If you are not seeing this, go into the RAID BIOS and set up the array correctly.
And last but not least, the most important and overlooked-the-most problem, are you using the correct driver? Sometimes you have to hit "pagedown" to see all the drivers on the floppy. There is no scroll buttons, and there is usually more drivers below the ones you see on the screen initially, and usually they are located down towards the bottom so you cannot see them without scrolling down using the page down feature.
And last but not least when you get it working, you better have a good backup plan. RAID is good, if you use a good backup.