If you review the requirements for the usage of Project Web App 2010, it requires IE 7.0 or higher.  Recently I had a situation where it was not possible to upgrade the Client from IE 6 to IE 7. So, I started hunting for alternatives.

Project Server 2010 SP1, offers some respite through multi-browser support, but it is limited to the Timesheet/Tasks page, and Project Sites. So, this only offers partial solution.

After much hunting, I found this option to install all IE versions in Stand-alone modes: http://utilu.com/IECollection/

Using this we can install several versions of IE side-by-side. So far, based on my testing things seem to work fine.

It is important to note here that this is not officially supported by Microsoft, so while there is some risk associated, this could provide a temporary solution until the upgrade could be done.