of course you can have two harddrives. all boards allow up to 4 drives (harddrives, cdrom, etc) total. other boards with built-in raid controllers allow more than that.
it looks like your new harddrive is already in and you have xp installed on it, i assume. since you have two optical drives and one harddrive, just set your old drive to slave, find a spot for it in your case, and connected the middle connector on the ide cable into it, along with power... and viola. should be good to go. in xp, just go into the folders on the old hd and drag over what you want to keep.