Hi,
I (only) have a 7D and was faced to the same problem. Everything has been fixed for me when I bought Cineform Neoscene: this software converts your Canon MOV files to AVI. Canon MOV files are known to have problems with Vegas. Also, they are compressed quite a lot, which involves a lot of CPU to decompress them and handle them in any tool like Vegas.
Neoscene is about 100$.
Alternatively, you may try ZoomBrowserEX, which is normally provided with your camera in the Canon utilities. This tool has a utility to convert MOV files to AVI as well. However, it looks like for me, it converts the files to 15 fps AVIs (while my MOVs are 25fps), which is definitely not what I want.
I am also rendering to m2t, and in the last 2 months (during which I used Neoscene), I believe I never had a crash any more.
And btw, I share your opinion about the Sony support… But I am quite enthusiastic about using Vegas (the Movie Studio Platinum version). I really like this tool (but was angry like you before using Neoscene).
Hope this helps,
Frederic