Long delays in attaching files (Vista+OWA+Cisco PIX)

7 of approximately 200 users on our network are testing Vista Business in an environment using Outlook Web Access with a CISCO PIX firewall. Attaching documents (even small) to an outgoing Email is taking up to 10 minutes. Replying to an Email which has more than a single reply also stalls. My laptop has no problem when used outside of the environment described above. Is the problem connected with (1) built-in VISTA security, (2) S/W-O/S described above, or (3) none of the above? Has anyone experienced this problem and/or does anyone have a suggestion?
My assistant, Dyanne, is working on researching the solution, you can also phone her at 610-363-9622, ext. 2229 or email her at Dyanne.Delaney@umly.org.
Thanks in advance for any/all advice!

I have done a little research for you. The problem actually lies in a combination of IE7 and Vista. One of the recommendations I read was to try installing Firefox and seeing if that takes care of the problem. To permanently fix the problem for using IE7, they suggest applying this hotfix to your Exchange Server. Here is a link to the thread I got the advice from. Good luck, hope this fixes the problem!

I use Vista and exchange 2007 OWA, and it works fine.

But I prefer Outlook (any version) over OWA.

The problem does not exist in Exchange 2007, just prior versions of Exchange with Vista used to connect via OWA.