|If you haven't set up a RAID array before....|
You have to actually set up the RAID array on the two drives BEFORE you install Windows.As in, prepare both drives for RAID use, after pressing the key while booting to access setting up a RAID array and doing that. Just selecting the type of RAID is only the first step.
Then, in your case of RAID 0, Windows Setup sees the two drives as one 250gb drive.
Did you do that?
The proper procedure is probably explained in your mboard manual.
If you did do that properly, I know from experience when you boot using the Windows CD and install Windows from that, Setup will successfuly get to the end of Setup even if the boot order settings are wrong, but once it's finished, if the boot order settings are wrong, THEN you will have problems - make certain you are booting from the first drive in the RAID set.
If the boot order settings are correct, you may have a display drivers or a display adapter related problem.
Press F8 repeatedly while booting, and from the boot choices menu choose Enable VGA mode instead of Safe mode or whatever.
Enable VGA mode loads everything normally except it forces the display adapter to use default VGA drivers that all display adapters and mboards support, instead of thespecific video drivers Windows is loading in normal mode.
If that doesn't get you to the desktop, try......
Press F8 repeatedly while booting, and from the boot choices menu choose
Disable automatic restart on system failure.
Choosing that boots the computer normally and should allow a blue screen of death to appear and stay, with a message on it you can investigate, rather than the computer rebooting before you can read the message.
That setting applies only once - only if you select it while booting - it does not "stick".
I don't know much about using RAID, but as far as I know you can't change the RAID type once you have made the array without having to re-install Windows. If you originally set it up as type 0, you should not change that.