RAID and AHCI question

Hello. I have a Gigabyte P35-DS3R motherboard and 2x500 GB Western Digital SE16 HDDs and 1x640 GB Western Digital Caviar Black. All drives are SATA.

Currently, I have Vista installed on one of the 500 GB HDDs and all the drives are running in PATA mode. I recently bought the 640 Caviar Black and I want to make this my main partition (running AHCI) while the two 500 GB drives are made into RAID 1. But the problem is that I have both 500 GB HDDs filled with data and I can't move them now. So, I want to install the OS now and a week or so later, I'll make the RAID.

Which option should I choose in the motherboard BIOS now: RAID or AHCI? Thanks.

Shouldn't make a difference.

Thanks.

Do you mean that I can just choose RAID mode in the BIOS without actually configuring any RAID at all?! Sorry. I have never done a RAID array in my life before.

Also, if I choose RAID, the other non-RAID drive will be running in AHCI or IDE?

You should be able to configure the first disk in ACHI and run fine. Then when you decide to set up the raid array set everything to raid configure the raid array in bios and make sure to use the other disk as the boot drive. Anyways you shouldn't have any trouble since your drivers will allready be installed and windows will treat it like a normal disk.