Jesse Toula posted Part 1 of Scripting for After Effects.
Check out also the 5-part series on scripting by Frederik Steinmetz, right here on AEtuts+.
For even more, see Dan Ebberts' chapter on scripting in Creating Motion Graphics With After Effects by Trish & Chris Meyer and a similar one by Adobe engineer Jeff Almasol for VFX Studio Techniques by Mark Christiansen, Lloyd Alvarez's AENY presentation on AE scripting, AE CS5 Help on Scripts and Expressions -- as well as the piled-on post Expressions & Scripting Resources for After Effects and AE Portal posts tagged expressions and scripting. By the way, Lloyd Alvarez has had an ongoing course teaching an Introduction to After Effects Scripting at fxphd.
Update: part 2 is up.