I have now sorted out my problems with my upgrade from 0.7.1 to 0.8.2
It looks like somewhere in this sequence:
start with s9y 0.6.x
upgrade to 0.7.1
move server from debian linux box to darwin/MacOS
upgrade to 0.8.2
either my allowoverride directives got trashed (or cleaned up by an admin) OR ...

Hmm it's very odd.
Finally got around to doing some double checking (setting the production variable to debug in serendipity_config.inc.php ) which means I went off to web-sniffer.net to see what the headers looked like.

I'm getting 302 errors which are pointing off into foo.example.com.
This ...

That was my guess too.
If restarting the PHP process doesn't work, if I delete all of the s9y directories then put it back in should I be able to get a working version?

Does upgrading the DB put out anything as part of the process?
I can't see anything in the "final" sucess page that actually says ...

Following from the RPC-XML exploit warnings I've done the upgrade.

Now I seem to be having problems getting anything at all out of my blog.

I'm still waiting on my ISP to kill and restart PHP incase some caching weirdness is happening, but I thought I'd post my results below.

I did get some ...

Hmm I found out what the problem was by using Mozilla and hitting stop as the error messages were in an endless loop (With IE it seemed to hang and stop didn't do anything). Once I'd spotted that the problem was with port 8080 I think all I did was change the port.
I was using PHP 4.3.4. If you ...

Yep, by default apache on NT uses port 8080. Change it to port 80 and it should all spring into life.
Don't forget to stop IIS if you have it loaded.

I tried chmod -R 644 as per the install notes and I got PHP errors, changing to 755 fixed it all, but my question is should I need r-x on the php scripts or not? The server is running mac OS-X and isn't hosted by me so I have no idea exactly how PHP & Apache were compiled or what flags are in effect ...

The bug is actually that serendipity doesn't work properly when the port of the apache server isn't port 80 (The default NT install uses port 8080).
If you use mozilla you'll get a chance to hit stop and see the results of the script running. Don't know if this applies to the Linux/BSD apache & PHP ...