ASP.NET MVC modal dialog/popup best practice
The jQuery UI library has a dialog widget that I use for things like this. While it's a plugin, IMO, the best practice is simply not rolling your own dialog widget.
Lunchy's dialog suggestion is nice. Just make an ajax request to your controller action and have the action return what you want to display, like a partial view with some formatting html. Then, put that html into your dialog, or whatever you plan to display, and show it.
One of the things that goes hand in hand with MVC is RESTful urls. That being the case the "standard" way of handling this would be to have the details pull up a new page with it's own, RESTful (and bookmarkable) URL instead of flying a dialog over the page. You could certainly do a "details preview" dialog within the context of the list, but if you're going to interact with the details, I'd consider doing a full request and get the details on it's own page.