<p>The "core" .NET languages are integrated into VS2008 - C#, VB.NET, and C++. I'm not sure about current support for J# and JScript.</p>

<p>But there are a number of other .NET languages out there - A#, Boo, Oxygene, F#, IronLisp/IronScheme, IronPython, IronRuby, Nemerle, Phalanger, P#, PowerShell, and <a href="http://en.wikipedia.org/wiki/Microsoft_.NET_Languages" rel="nofollow noreferrer">more</a>. Of these, I have only found VS support for F# (which is made by Microsoft, so no surprise there), Oxygene, A# (but only VS2005 support), and IronPython (only with external projects designed for this purpose).</p>

<p>But what about the other languages? Since they target the .NET runtime, I figure that it only makes sense that there would be a way to use those languages inside VS. Is there some limitation(s) of Visual Studio that prevent this? Is there a way to "force" VS to compile these languages?</p>

I suspect it's pretty simple: IDE integration is no simple task, if you want to do it well. I would guess that most of these languages are done in spare time rather than having commercial funding. The amount of effort required is just prohibitively expensive - and not necessarily due to Visual Studio making things particularly hard, but due to it fundamentally being a difficult thing to achieve well.
That's not to say it can't be done, of course - just that it's hard, and "hobby" projects aren't likely to get that level of commitment unless they're really popular.
For Boo, by the way, you should look at
BooLangStudio
.