Does anyone know a windows app that lets you test a site in different versions of IE ?
Try Multiple IE's.
However i believe that only supports up to IE6.
For 6/7/8, the only one i know of is the Microsoft Expression Web Super Preview.
I find the best way to do this reliably is by using virtual machines with different versions of IE on each one.
Here you can try this one. Heres a review which talks about how ie tester and multiple ie's are not that great as like you said do not render the webpage properly and that there were some problems specifically with multipleIE's when it came to forms on the webpage. so since then theyve been using a software called IECollection. Heres the review/report kind of thing: http://stellapower.net/content/multiple-ies-including-ie8
So theres something called IECollection. And you can download it from here. Check it out. http://finalbuilds.edskes.net/iecollection.htm It might be the long way but it definitely does the trick.
Let me know if this helps
PK