This build… I honestly don’t remember it all. Just check the change log on the forums. :P

To recap: there is only one download (found at the bottom of this post); This file is the universal install for client and server; it no longer goes in the jar.
Mystcraft goes in the mods folder.

If you are still lost on the 0.10 series, check out Direwolf20′s Mod Spotlight! Direwolf20′s Mod Spotlight for 0.10.4.00
If you are having trouble with writing, check out Direwolf20′s Writing tutorial!
Note that there are a couple changes between the video and the current mod, particularly that colors and things are easier to write. If you follow the tutorial, you’ll do great.

Download: [1.6.4] Mystcraft Universal 0.10.13.00
Download: [1.6.4] Mystcraft API 0.10.13.00
Check the Mystcraft Forums for updates and the change log.

Enjoy!