Couple of questions about a HD

Hello Geeks.

I just installed a new (well, technically not new, but new to me) HD into my computer. I have a mini-ATX case (I think that's what it's called...it's not the same size as a regular tower case), with only 3 2.5 (floppy size) drive bays. I installed the HD into the middle bay, with the bottom and top bays occupied by the old HD and the 3.5 floppy-drive, respectively. I'm running HD Health monitor, and it's telling me that the bottom HD is running at a temp of 47 degrees C. Does that sound OK?

The HDs in question:
(newly installed) Maxtor 52049H4 20gig 7200rpm ATA/100
(old) Maxtor 6Y080L0 80gig 7200rpm ATA/133

Also, the newly installed drive is a ATA/100 while the old drive is an ATA/133. What does that mean? The newly installed drive is rather noisy (but doesn't seem slow)...so, is that what it means? Or is the noise due to the fact that it's (age wise) an older drive than the old drive?

Thanks for your help.