OP: if you not choose the SSD and go for a normal IDE drive, than I recommend you try to find out the noise before, so you won't have to do the operation again.
I replaced my ibook G4's Toshiba 4200rpm 40GB with a WD 320GB blue with 5400rpm and although the datasheet says it is much quieter it seems louder to me. Sound is very subjective, dB does not actually say whether you will find something noisy. Example: some will find high noises noisier, others a deep grumbling or the vibration on the desk.
I have researched a long time for the speeds, when I made the decision and I can second California's statement, the WD 250GB and 320GB and the Samsung 160GB seemed to be faster than the Hitachi 7200rpm 7k100. The Hitachi was last produced in 2007. While the Samsungs and WDs are still made. When you look for used ones be sure, that the WD does already have the blue badge and the Samsung is the HM160HC (one Platter) not HJ (two 80GB Platters).
I unfortunately did not determine noise for myself, since everyone in Forums said they were both very quiet (and very energy saving). I will put my ear on a Samsung one, if I have the time again and get hold of one cheap (HDDs prices have grown a lot in the past two month due to production loss, because of floods in Thailand and at least WD is short of supply (the others just take the extra money it seems, since not every manufacturer has production facilities there).
Personally speaking I can say, that the fan does turn on much less with the WD 320GB and my left hand palm does feel the drive does not get that hot like the Toshiba did.
As others have already said, the higher density will make the newer drives faster than the Hitachi and it is quiet expensive on Ebay compared to the others.