I would not put a 7200RPM drive in any laptop of mine again. My MBP just got to hot with a 7200RPM HD and i believe that part of the reason why it got to hot was because of the HD.
When i got another CD MBP that came with a 5400RPM drive the drive was pretty silent and my laptop did not get as hot.
I have a Seagate 5400.3 PMR HD my iBook overall it is a pretty silent drive but i can hear it at times very faintly but it is not loud. Relatively it is still a pretty silent HD. I was completely spoiled by the iBook original Fuji 4200RPM drive that was in my iBook as that was completely silent and i could not hear that at all. I have read that Fuji do make pretty silent HD's.
I have also read that Western Digital make the most silent HD's that you can get but the Seagate HD's are faster especially so the (PMR's) ones but they are supposed to be not as silent as the WD HD's. I have also read good things about Samsung Spinpoint HD's as well.
This link maybe quite useful
http://www.pcpro.co.uk/reviews/90550/toshiba-mk1234gax.html
The 5400RPM drives are in my experience pretty silent HD's but the 4200RPM drives are the most silent HD's you can get i would say.
I upgraded my ram as well to 1.5GB i got a good deal on a 1GB new stick for £25 on Ebay.
I have the 14 inch last revision version that comes with a DVD-RW and this is the part that is used in my iBook TEAC DV-W28SLA.