the 64-bit version of Internet explorer is in C:\program files\Internet Explorer\iexplore.exe
the 32-bit version is in C:\program files (x86)\Internet Explorer\iexplore.exe
they both run fine here
and I was curious so I wrote a program to check, that looks at the PE header flags. the one in Program Files is 64-bit; the one in the (x86) folder is 32-bit. That being said a 64-bit application will only run faster then it's 32-bit counterpart if it takes advantage of 64-bit features. Don't know if IE64 does that; not many programs do, actually.
Minefield won't work with most of my Firefox plugins... like adblockplus... which is the reason I don't use it as my main browser.
They are 64-bit... but there is no reason to use them at all over the 32-bit versions. So much so that the 32-bit version launches by default on Vista x64.