Welcome to NICO! Sorry to hear about your problems...but they actually are common issues with older G's.
For the AC/Radio, you need a new control board. Check out this website that has done a ton of replacements:
http://www.shortcircuitrepair.com/
Drivers' window: try the reset procedure (search the board/FAQs)...if that doesn't work, try to replace it yourself so save some $$.
The Transmission: sounds like a syncro problem...only fix is a new transmission. They say it might fix the problem because it's an issue with most manuals...if it's out of warranty, I'd just live with it.