Is Haskell for Visual Studio 2005 compatible with VS2008 SP1 ?
I actually had just tried to install it from the link you provided (yesterday), but the installer complained that it couldn't find an existing installation of Visual Studio 2005. (I also have Visual Studio 2008 installed.) I'm guessing it's hard-coded to look for a specific directory or installed application version number? So... from what I've seen, I'd answer "no".
Hopefully someone else has had better luck?
I was told at a conference in 2007 that the Russian student who had been working on Visual Studio support for GHC never quite finished the job. The person most likely to know the true status is Simon Marlow at Microsoft Research.
The answer to your original question is a No. The code for visual haskell is written in Haskell and talks via COM to visual studio. Now the problem is, that even if you update the com wrappers to be compatible with the new visual studios you'd still be stuck using a ghc 6.6 simply because it relied on internal structures of the compiler to work, some of which have already been removed from 6.8 going forward.
So any effort on this part will require a complete rewrite of plugin.
Now the good new is I am busy writing a version for visual studio 2010 (sorry no 2008) but supposedly I could release it as a standalone isolated shell for those who don't have vs 2010 (need to check the license more closely).
I only have time to work on it in the weekends, So I project (no promises) that I'll have a first version out around july.