> I'm a lvl 13 cleric. Abjuration, alteration, evocation are AT LEAST at
> skill lvl 60, and probably divination and conjuration are pretty high as
> well. How can that be explained?

The skils you speak of are a seperate set from the actual 'specialization'
skills. In other words if you look at your skill list you would see
Abjuration as a skill as well as a skill named Specialize Abjuration.

>
> I haven't noticed any better casting ability in any of my spells. How can
> that be explained?
>

You arent specialized yet.

> If I HAVE specialized, how can I tell which one it is?(they went over 50
> about 3 weeks ago...I don't have a clue which was first).

See above.

> If I HAVEN'T specialized, how do I do it?

You have to be level 30. Once you reach level 30 go to a cleric guild
find an NPC who can train you and look for the boxes labeled
specialization. There should be one specialization box for each type
of skill.
It doesnt say which casting type you can specialize in on the box but if
you select one the guildmaster will say something (I dont remember what
it is exactly they say) which will have the name of the type of spell
that specialization applies too. (Alteration, Abjuration, etc.)

> If I HAVEN'T specialized, what happens to the other 2-4 spell classes that
> have already gone over 50? Do they stay at 65, or do they drop back down?

This isnt how it works, see above. :)