It must be a browser issue (specific version that you are likely using). I use both an XP and Windows 7 and it usually works well on FF on both these machines.
You can turn on the trace for ISC to see some happenings on the server side.
I would try the steps under manually collect data from the must gather
http://www-01.ibm.com/support/docview.wss?rs=0&context=SSCPPRK&q1=MustGatherDocument&uid=swg21199337&loc=en_US&cs=utf-8&lang=
and view the trace files to see what is happening on the server side.
This is not going to get you further as the server side does not seem to be the issue. It is worthwhile looking at the logs/warnings from the browsers in Windows7. That would give us clues on what is happening. This is still worth doing to satisfy ourselves that the browser is making its request(s).
Give Chrome a try and see if the ISC shows up on Chrome in Windows 7? What are the specific versions of FF and IE that you are use?