1.) The MOBO should have a manufacturer's symbol on it somewhere; it might be difficult to find though.
a. Is this a pre-bought computer (versus one you put togethre yourself)? If so, can you get the model # of the computre?
b. what color is the mobo itself? maybe someone will recognize it by the color scheme.
c. Can you provide the approximate year the computer was made?
d. Can you post a picture of the mobo and your computer? (use imageshack, picasaweb, photobucket etc.- sites that will host your pictures on the web; I'm assuming you have some form of broadband internet access.)
Those leads may be ways of tracking down the model of the MOBO.
2.) Is anything printed around your sata ports on the MOBO? You may need magnification.Each of my computers have labelling on the mobo around the different ports and pin connections. For example, my MOBO has 4 sata ports;2 are orange, 2 are purple. Each port has 2 "outlets" (for lack of a better term). If I plug my sata cable into the left orange plug, right side outlet, the bios reads the drive as primary 1. If I move the cable to the left orange port, left side outlet, bios registers the drive as slave 1, etc. etc. with the numbers moving from 1-4. The other difference is (using my mobo as an example) that each color sata port is controlled by a different chipset. On the mobo to the right or left of each SATA port is tiny writing identifying port numbers 1-4. Maybe yours has this.
3.) do a search in the forums for "raid"- there are some really good posts that offer more detailed information about setting up raid. With 2 drives you can mirror in Raid 0. One drive will copy onto the other so you will have all of your info backed up, but will sacrifice the capacity of the 2nd drive. Instead of 500GB (250+250) you will only have 250GB available in the raid array. Your 3rd disk will still be available as normal.
With 3 disks, you can do other raid set ups, but that's up to you whether or not you wish to do that based on whether you place higher value on sheer speed or reliability.