There is a version of Internet Explorer for Intel Macs, if you want to install X11:
http://www.kronenberg.org/ies4osx/
It is not the official version, but may be compatible with some websites that the last official version is not. X11 may be extracted from your Mac's original installer discs. I've attempted to locate the article on how to do that, but can't find it at the present time. If you need help finding it, I'm sure someone in the Developer forum can help you:
http://discussions.apple.com/forum.jspa?forumID=727
In the meantime, if you just want to see what a website looks like Internet Explorer,
http://www.browsershots.org/ offers a nice service to do this without having to install any new software.
If you find a website that says it can only be used with Internet Explorer, please point the webmaster to
http://www.anybrowser.org/ They obviously don't know how to code websites for the greatest amount of customer support, and need to understand there are ways of making websites compatible with all browsers.
Additional info can be found on my FAQ*:
http://www.macmaps.com/browser.html
- * Links to my pages may give me compensation.