Our site is migrating from MovableType to ExpressionEngine, and there is one small issue we are having. MT uses a date based URL structure, e.g. www.site.com/2012/03/post-title.html, while EE uses a category based structure, e.g. www.site.com/index.php/news/comments/post-title. The issue is that our MT page used Disqus for comments, and as such comments are tied to a specific URL, meaning that we'd lose all of our comments if we were to migrate. I am wondering if there's a way to change the URL structure in EE to match MT's, thus allowing us to keep the comments. Thanks in advance.
Correction: EE uses a Template Group/Template based structure for URLs, not categories - just to clarify.
You've got a couple of options here.
One is to create an .htaccess rule which internally redirects all requests matching YYYY/MM/ to your EE template which displays your posts (say, /news/entry/). I don't know exactly what those rewrite rules would look like off the top of my head, my mod_rewrite-fu is pretty shallow. But it could definitely work.
Another is to export all of your comments from Disqus via their XML export tool, then do a grep-based find and replace using something like BBEdit, replacing all /YYYY/MM/ strings in that file with /news/entry/; delete all of your existing comments on Disqus; then import your newly-modifed XML file.