IE9 32 bit version got a newer and much faster java engine. So even if it sound logical to use the 64 bit version of IE9 the 32 bit version are faster. So basically i would say that the 64 bit version og IE9 are useless.
Not sure what happen when you post in this forum with IE9 since you didn't include any details, but if the post is blank there is an announcements at the frontpage of this forum that says:
Users of Internet Explorer 9 are experiencing problems creating posts and private messages. The content is lost and appears blank when posted. While this is being investigated and fixed, please use Quick Reply, Internet Explorer 9's Compatibility View, or an alternate browser to post.
So to use IE9 here you have to enable compatibliity mode for this forum in IE9 or use quick reply. To use compatibility mode for this forum just click the compatibliity mode button when you visit this forum and it will be default on the next time you visit this forum.
Seems like the IE9 x64 crash is already discussed here:
I had the same problem where IE9 64 bit would crash, but there is a workaround. Follow the steps below and it should solve the problem. I didn't have to reboot so i just skipped step 6.
1. go to: http://technet.microsoft.com/en-us/sysinternals/bb963902
2. Download & install autoruns app.
3. run AutoRuns
4. on AppInit tab, find:
NVIDIA Compatible NVIDIA shim initialization dll, Version 270.61
NVIDIA Corporation Un-check it (do as administrator in case you run windows 7)