In broad outline, I agree with Richard Urban. IE7 is an integral part of
Vista, it cannot be replaced or downgraded to IE 6.0. But because your
app is a work-related Peoplesoft application, upgrading or replacing it
with "something that is up-to-date" probably won't be a straightforward
matter. You'd need to get your IT department to work with Peoplesoft, to
get a replacement or update compatible with Vista.
I had a similar problem, which I solved by with Microsoft Virtual PC
(it's free! download and install it from
http://www.microsoft.com/windows/products/winfamily/virtualpc/default.mspx).
I created an XP virtual machine. When I need to run my financial
application (which is incompatible with Vista) I just fire up the VM on
my Vista desktop, and run it there. Cut-n-paste to the host Vista
session is seamless, and files can be swapped back and forth via a
shared folder.