The computer has no floppy. I am slipstreaming the drivers with nlite, but during the start of install windows says it can't find any drives and cancels the install. The card bios screen shows the drives so they are there.
I have not used this card, but I have used RAID1 built into BIOS on a mobo. In that system there are two steps to take before the RAID array can be recognized and used. First, when you boot, you go into BIOS Setup and find the place to set the mode for the drives. In your case, these two drives on the add-on card are the only drives in your machine, and they are IDE. (I am assuming that you followed the card's directions for how to set the two drives' jumpers for Master or Salve positions.) I assume further that, with this card in place, there is a screen or two added to the original mobo-based BIOS that shows additional options for the drives attached to the card. It is probably there, following the card's instructions, that you set the drives' modes to be RAID devices.
Now, on a mobo-based RAID system, it is common at this point to Save and Exit to save those BIOS settings. Then, as the new boot process runs, there is a screen prompt to press certain key(s) to enter the RAID Configuration menus. In your case with the add-in card, I am not sure whether you get to this in the same manner, or whether the RAID Configuration options are done within the "normal" BIOS Setup screens. Either way, you probably have to make some RAID setup choices: Which drives will be assigned to the RAID array, what type of RAID is this, some RAID parameters, etc., and then actually proceed to create the RAID1 array and "initialize" it. Then exit. Until that array is created and initialized, Windows Install will not be able to deal with it.
You are slipstreaming the RAID drivers into your Windows Install disk, I understand. That suggests to me that you have XP to install. I was going to ask if you have the right drivers, but you seem to have checked that already.
IF you are working with XP, what version are you starting with? The original XP could not handle HDD's over 137 GB because it lacked 48-bit LBA Support. You MUST have at least SP1 installed, and certainly SP3 is preferred. If you have NO Service Pack included in the Install disk, you must find a way to get SP3 added into the slipstream version you are preparing.
IF you are working with Vista or Win 7, be aware that both of those are supposed to allow you to load device drivers early in the Install process from external devices OTHER than floppies. Specifically, you can use USB memory "drives" if your mobo supports that device, or you can use an optical drive as the source that Windows searches for drivers. If you can do either of those, you will not need to slipstream anything to get Windows to install.