Motherboard ATA66 adding ATA100 PCI card

I havea MSI Motherboard which is ATA66 maximum and have purchased a ATA100 drive. I have now purchased an ATA100 PCI card and want to install it. Problem I don’t know is, when you install the card and connect the hard disk to it (which at present is the C: drive and boot drive) what is the letter of the drive if I connect the current c: drive to the new ATA100 PCI card. My bios dosen’t allow for more than 2 hard disk, CD or zip drives.