Hmmm...I'm using Mozilla Firefox (3.0.5) right now as I type this and it seems to be working fine on my Vista 64 machine.
As for Flash, yeah, it's not compatible with Internet Explorer (IE) 64. Period. With that said, I doubt that the program will even work on Vista64, even "if" you managed to get it installed. Check with Adobe forums, but I'm 99.99 percent sure it won't work, or install, under 64. Now, If you want to view
flash objects in IE, you'll have to use the 32-bit version of IE which can be found in your "C", "Program Files (x86)", "Internet Explorer" then click on "iexplore.exe".
You can create a shortcut by right clicking the exe, then choose "Send to", then from the dropdown menu choose "Desktop (create shortcut)" Now you have the shortcut to the 32-bit version of Internet Explore on your desktop.
Hope that answers your question.
Note that this post was submitted using Mozilla Firefox.