I'm having the same issue. I have looked around on the forums, but can't really seem to find a solution. Here was my sequence of events:
I downloaded 5.0.1. Install version today.
Put the files in a directory on the web server.
Set the permissions on the folder to have ASP.NET have full control.
Configured the directory in IIS for the application pool.
Ran the install, had a "ScriptHandler" isssue in the web config.
Removed line 90 from the web.config
Ran the install again, and it went through the process.
I clicked the link to go to my site and got the .../Default.aspx?tabid=38&error=Object+reference+not+set+to+an+instance+of+an+object.&content=0
This is an XP machine, IIS 6.0, with .NET 3.5 installed.
Any suggestions?
John