SATA Hard Disk problem

I am new to SATA. I have installed two 300Gig SATA HDDs in a new PC I am building. Unfortunately, only one of them shows up in “My Computer” as drive C: How can I get the other HDD to show as drive D:?

For the first time in my adventures with PCs, I tried setting up RAID with the two HDDs. My setback is that I need to boot the PC initially with an “XP startup floppy disk with CD-ROM support” Can somebody out there help me with such a disk or direct me to where I can download it from?