First: Sorry for my bad english and thank you for this wonderful thread!
My Game still crashed BTD when I'm zooming in or out. So I deleted my hole Plugin-Folder and re-download (for my opinion) the most important files, but the game was still unplayable.
I spent some time on testing out, and now this will work fine at my PC: (Core2Duo E6400, Asus Mainboard with onboard sound, 2 GB RAM, Geforce 7600GT):
I had defrag my my harddrive and set the virtual memory on 4GB on C:,
I changed the "Graphics Rules.sgr" like the way on this site: http://simcity.ea.com/help/faq.php
I run the game with just 1 Processor (open the Taskmanager after starting the game, rightclick on the SimCity entry and set it on single processor)
Now my game will run fine with nearly 2 GB in the Plugin folder.
Thank you, people!!