Our SDK SP1 can be found up on the insider site in the Developer's Corner, on the Downloads page and at the Microsoft Download Center. It contains a full set of tools for Gmax (including some new scripts, the updated attach point tool and animation manager and the LOD and name tool), as well as a bunch of updates and fixes for 3d Studio Max, sample files that actually work for both (including scenery, aircraft, animation, skinning, materials, etc.) and a whole mess of new documentation.
A quick note about setup: read the documentation. Everything is set up very differently from how it's been in the past. You shouldn't need to move anything around anymore. It should all work where it is installed if Max and Gmax are setup properly. This is because of all the new dependencies on files like the modeldef.xml file and the new FS Tools menu. So if you're getting missing script errors, read the setup documentation, it will explain where to point the plug-in path for Max and Gmax.
Hope you enjoy, and now we'll get to work on SP2. ;)