I have pought and used two Maxtor drives of different sizes - not as big as 120 though. However, in all case I have been very pleased with the performance and ease with whic they were fitted and formatted.
If I remember correctly from the documentation, Diamondmax use 40gb platters so an 80gb drive will have just the one platter with two heads. [One on top the other underneath]. This is useful to remember when partitioning for example.
Your 120 will have two platers but only three seek heads, the first platter will have two heads as above, the second will have just the one head reading 40gb.
Seeing as you will have the underneath of the platter doing nothing, it may be a good idea to price the difference of a 160gb drive to gain the extra seek head and use the underneath side of the platter that is already there.
I have exactly what you are enquiring about, I have had it for about 18 months now,it was easy to install and I have portioned off to make 3 drives.
If you buy the boxed version it comes with maxBlast3 installation software CD and manual which is a doddle to use.
It's very quick and very quite!!
Note,if you are going to use in conjunction with an existing hd, make sure you have SP1 (if xp) because your mobo will not recognise any data past 137gb (137gb bios barrier)all this is explained in the manual.
I have an 15Gb 7200rpm IDE,its brilliant.I have also got 2x120Gb SATA hdd's,they have been a real pain.I have just spent the last 48Hrs reinstalling XP onto them,they are supposed to be faster than IDE but this is only true in windows,it takes hours to format a 10Gb partition,and I gave up waiting for DI to reinstall an image(Caldera DOS)as having waited on a previous occasion for 4 hours it then locked up completely with 2% left to do.