Help!! What happen to the hard disk partitions???

I want to reformat my hard disk. I have 2 hard disks, one 80 GB the other 200 GB a total of 6 drives. WHen i put in the win XP installation CD and wanted to reformat only the C: , i could only see my C: at the installation window. WHat happened to my other 5 drives? The C drive was initially 40 GB, now it shows that it is 280 GB, which seems like all the drives had merged together or something..

What happened? Why did all the drives suddenly becomes one?

HELP!! What shld i do? If i format the C drive (if the drives are really merged, unknowingly), all my data will be gone!!