If you are going to use Google Apps account in pidgin you have to use a few tricks to make things working:

In Basic tab:

1. Change Domain from gmail.com to yourdomain.com

In Advanced tab:

2. Remove check “Require SSL/TLS” and set “Force old (port 5223) SSL

3. Change “Connect port” to 443

4. Change connect server to talk.google.com

This should do it. Here is a screenshot from my working setup: