I see no one has replied to your request. I've always had to do some bit of maneuvering to get HelpStudio to agree with TFS. We recently moved to TFS 2010 and when I first opened HelpStudio, I was somewhat distressed thinking that it just wasn't going to work with TFS 2010.
I think I now have it talking to TFS 2010, though I haven't worked with it much. I have VS2008 installed on the machine that Help Studio is on. Before it would do anything with TFS 2010 I had to install the "Visual Studio Team System 2008 Service Pack 1 Forward Compatibility Update for Team Foundation Server 2010". You have to install this to get VS2008 working anyway.
Once I installed that, Help Studio seemed to connect to TFS 2010 (using the same url you have to use in VS2008) and was much happier. My projects were not connected any more (remember we came from TFS 2008). I basically had to remove them (using VS 2008, be careful TFS will delete your local copies) and add them back in (in Help Studio). Help Studio still complained and didn't connect the project up, although it did put it into source control. I ended up having to open the project from source control, after that everything seemed to work.
In retrospect, you might not have to delete the project and add it back in. You may be able to hook it up by opening it from source control, but I didn't think of that until after. Also, it might work fine if VS2010 is installed on the same machine, I didn't try that either.
Good Luck.
Bill