Hey, guys,

Sorry if i overlooked this been already "uncovered" and solved,
bit i found a way and wanted to share it with you anyway.

So, here's how i managed to workaround this same issue that drove me nuts

1. Pop in your Snow Leopard DVD
2. Open up a terminal, sudo -s + password and copy/paste in following lines:

cd /Volumes/Mac\ OS\ X\ Install\ DVD/System/Installation/Packages
installer -pkg /Volumes/Mac\ OS\ X\ Install\ DVD/System/Installation/Packages/BSD.pkg -target /Volumes/Your_Drive/Library/Receipts/
I gave the direct path to the proper place of the receipt, but i think it should be working when giving the root "/", too.

3. Result :
installer: Package name is BSD
installer: Upgrading at base path /
2009-10-04 14:50:28.344 installer[451:742b] using receipt prefix of /
installer: The upgrade was successful.
bash-3.2#

4. Go to Disk Utility and successfully repair your permissions

Hope this helps,
Greetings