Okay well if you dont hear a click then the solenoid isn't engaging.......this is the first thing that needs to happen to start the car. The solenoid pushes the starter gear inwards to engage with the flywheel. If this doesn't happen then the starter cannot turn the engine over. The starter motor itself however is probably fine because it shouldn't be engergised until the solenoid has done its job.
To start by sucking eggs the first thing to check is the battery! Even if you can measure 12volts accross the battery with a meter it may still not be able to supply the current required to operate the starter however it would need to be very flat I should think to not get as far as engaging the solenoid.
So step 1 is to try jump starting it.
If you know that the battery is fine then move on to the starter/solenoid itself, from the pictures posted earler you can see that it is attached to the side of the starter. Things that can happen here to prevent the starter from engaging could be the solenoid/starter has a mechanical fault that stops it from engaging or it may not be getting the required juice from the battery due to a poor connection somewhere or it may have an internal electrical fault.
Mechanical faults due to wear and tear normally show up as intermittent faults that get worse with time for example if the bearings in the starter wear then it may not engage properly because the armature is dragging on the housing. In this case sometimes it can be hit with a hammer whilst an assistant turns the key and persuaded to start! (yes there is a place for percussive maintainence in fault diagnosis!)
On the electrical side there is only one connection on the starter/solenoid you need to check and this is the smaller of the two and probably a yellow wire. This provides the live feed to the solenoid via the keyswitch and fusebox. If everything works then when you turn the key 12v should appear on this wire. If it does and you've tried all else and the connection is tight then you need a new starter/solenoid assembly. Check also that the starter/solenoid assembly is bolted tight to the bellhousing as this is where the system gets its earth (negative) connection. If 12v does not appear then check the fuse and the keyswitch. You can eliminate the keyswitch quickly and easilly but I'll PM you that information as it may be useful to theives so I dont want to publiscise it here. If the keyswitch and the fuse check out then there must be a break in the wire somewhere, you can narrow this to before or after the fuse by seeing if you get 12v at the fuse when the key is turned, no doubt by this stage you'll be calling an auto electrician though.
The following links are great indepth info on mechanical workings of the starter and a good wiring diagram that you can strip layers away from and view the starter system in isolation (select starter and battery)
http://www.hillmanimages.com/912/lect15.html
http://www.hillmanimages.com/912/early_912_wiring.pdf
both give more info than you need to know though.