SharePoint and 64 bit stuff
I was recently troubleshooting some IE issues with a customer when I discovered they were using 64-bit IE clients, ..., yes I was surprised too. So for those that may not know, only 32-bit IE 6 and IE7 are supported by SharePoint, as you can see from the link below:
AFAIK, only 32-bit ActiveX controls were shipped with the Office clients to provide SharePoint integration, which means only 32-bit IE can take advantage of those ActiveX controls. 64-bit Windows provides both 32-bit and 64-bit IE.
One other tidbit, keep in mind that the next version of SharePoint will require 64-bit servers, check the link below for more info or just check out the exerpt below...
Recommendations for 64-bit hardware
Windows SharePoint Services 3.0 and Office SharePoint Server 2007 are the last SharePoint Products and Technologies versions able to run on 32-bit hardware and operating systems. Do take this into account in current and future hardware decisions: Buying 64-bit hardware today helps ensure that your environment can accommodate future requirements and helps you to take advantage of the performance and scale of 64-bit technologies.