Replacing the hard drive on my notebook...

Well, the specs (from Samsungs webpage or elsewhere) suggest so (notebook HD), but you have to remember: laptops (and certainly Apple’s) are manufactured tightly, so that eg heat flow is very precisely regulated for the original drive. Replacing something like a HD may mess up the heat flow. So a heat problem (if any at all) would be in the configuration as a whole, not the HD by itself.
For starters, you could try and compare the temperature specs for the old and new HDs: if the new one releases much more heat, the iBook may simply not be able to cope with it properly.
You could search for other people having done something similar, and what their results where.

Yep, certainly hotter. What do you think will happen if it does overheat? Would I need an whole iBook replacement? Also the hotter HD used to be in a 2.5” enclosure (exact size, so it was tight) but it didn’t feel as hot. Is there a thermometer inside my ibook?

You can use iStat Menus from http://www.islayer.com/index.php?op=item&id=28 to check the temperature of your hard drive.

As a metric. The drive in my iMac is running at 110F. The CPU is at 112F and the optical drive is at 92F.

Yeah, the temperature is just a little bit hotter… but now I realized that my HD doesn’t seem to ever stop spinning. (at least it doesn’t sound like it stops) is this a software problem? (like the OS)

hmm, there’s a difference between the HD spinning, and the fan spinning when trying to cool it. What happens if you put your iBook to sleep (just to be sure, leave the lid open, so it can cool a bit more via the keyboard part)? While I guess sleeping also silences the fans, those may going ‘round a bit longer to cool the last bits.
But never stops: if you leave the iBook alone for an hour, with absolutely no programs running (ie, the login screen after a boot, or your desktop after a boot), it’s still noisy? (keep it in a cool place, outside any sunny spots, just to be sure). That would more likely point to a software problem, since there’s no particular reason the hard drive would be too hot in such a case (although, if it’s a new HD with a new system install, spotlight might be updating it’s database in the mean time). If that’s the case, Apple may not have the appropriate drivers (or at least no optimised ones) for that hard disk.

Yep… just spotlight and google desktop doing its thing. I can now here the fan, but the HD stops when its not in use, also IS there a way to get optimized drivers for the HD?