It sounds like the BIOS and hardware are correctly set. Where you say:
"Adanced bios features" : "hard disk boot priority" we got
1. "SCSI-0 : NVIDIA STRIPE 306.77G" first and
2. "bootable add-in cards". this is correct, isn't it ?
This implies that the RAID stripe has been identified and recognised perfectly by the MOBO.
NOTE: When set up as a RAID array the BIOS does not "see" the array as IDE disks in it's POST startup checks - effectively the hardware RAID device makes the array look like a single SCSI HDD to the Mobo, in your case, SCSI device 0.
So the problem seems to be getting Windows to recognise the array at start up!
I believe the drivers you already have (i.e. from NVA020.zip) ought to work. Presumably you extracted these to a floppy disk? So when you press F6 while Windows boots, then press "S" to add a driver at the right time, you should be presented with 2 driver options - one the NVidia Parallel or Serial "ATA Controller" and the other the "ATA RAID Class Controller" (or similar description).
EDIT - NB - If you wanted to try the drivers from the 30mb NVidia executable file (drivers version 4.27), you can open the ".exe" file using Winzip or Winrar and then find in the list of files the subdirectory for IDE/WinXP drivers. Ensure you select all these files, and then extract them to a directory and coppy them to a floppy.
Have you loaded *both* the drivers before installing windows?
I think both are needed for Windows to recognise the array. Basically, you add one (I don't think it matters which is first) and then press "S" again and add the other.
Does this do the trick?