Hi Jon,
I recommend, right click the top level folder and choose TortoiseSVN > View Log
Then in the log right click the entry for revision 6393 and choose revert to this revision. That is the last revision before the change to VS 2010. After that I would not do svn update again until you are using VS 2010 and have updated your custom projects to it. You may have to convert the mojoportal propjects as well but then you can revert and then do svn update to get the versions already updated.
The VS 2008 solution and project files are going away very soon, so I would move forward with VS 2010 or the free Visual Web Developer Express 2010 asap.
Hope it helps,
Joe