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,

-Lukasz