did you just copy a bunch of files, or run programs from those hard drive(s)? that seems a bit hot, but not "insanely" hot. I wouldn't worry about it. besides, I have three of those Maxtor 160s, and I can definitely back you up on them getting hot. VERY hot.
edit: yeah, like the above person said, definitely get some fans in there. I have:
160
160
160
120
80
hard drives. 5 total. I put four 80 MM fans in front of them (attached to the front of my case) and if I need something that is hard drive intensive, I crank the fans up to full blast.