Hey there snowcrash,
If you do decide to tackle the evaporator core, here's a write up (of sorts) that may help you:
http://www.justanswer.com/pontiac/21vxe-remove-a-c-evaporator-pontiac-grand-prix-1999.htmlNo pics, but it has an "ask the mechanic" feature if you need more detailed info. Hope that helps, and best of luck to ya!