There are a couple of threads on the Reporting Services MSDN Forumn and newsgroup about IE 7 Beta 3 freezing when trying to view Reporting Services reports.
Just wanted to put some quick info out for folks who run into this issue:
Firstly, we know abou the issue (we too hit it in our internal testing just not in time to catch Beta 3). It only affects IE 7 Beta 3. Beta 2 is fine.
Secondly, the IE team is working on a fix to the issue for us. It will show up in later builds of IE 7 as they become released for broader testing.
Take care and good luck,