I just ren into this Internet explorer testing engine for Windows Vista. A standalone application to test multiple internet explorer versions.
Download the newest version here
Awesome stuff!! Finally I am able to test my websites for stone age explorer browsers which are still used by 25% of my visitors..
and all that in a nicely designed standalone application.. hallelujah
Much love to my sister for mailing me this :-)

Peace Ya’ll
ietester
Ps. Producers of the IE6 Standalone

Another great tool is Adobe Browserlab which has an awesome onionskin overlay tool by which you can your nightmare visible whit the upmost detail. There’s also a Dreamweaver plugin available which probably has some nice features also which I haven’t discovered yet.
Adobe browserlab - cross browser compatibility testing

I was also made aware of Browsershots dot org.. but it’s crap.. like most online browser compatibility checkers, with a lot of irritating advertisements and bad design.