dave_d,
I have tried an upgrade and a fresh install and the PPTP vpn never works for me in 5.6 or 6.
As far as your upgrade situation, personally I like to back everything up, ghost the hard drive to another drive if you can, and then perform an upgrade on the newly ghosted drive. If it works, woohoo, you have a lot less configuring to do. If not, then you did not really lose anything. Just do a fresh install if the upgrade does not work.
I just upgraded a working 5.5 box to 6 and the vpn no workie no more.
Funny thing, I pulled out a HD that I had put 5.6 on about a year ago (one where the vpn would not work), booted up the machine, and then I could vpn in, go figure! Of course it did not last long, today it will connect but just hangs after that.
Oh well, I am really bummed that this problem is _still not fixed_,

steve