[tmedwards]

For GCA4, sheets are written in VBScript. Beyond looking at existing sheets for examples, and asking questions around here, your best bet is probably these links:

• Scripting @MSDN - You can find docs on VBScript and WSH here.
• VSView8 @componentone.com - GCA4's print engine. GCA4 actually uses VSView7, however the differences are trivial.
• GCA Character Sheet @GCAWiki - Lists most of the various interfaces sheets can access in GCA4.