Don't ask me how this happened but I've already wasted 2 days fixing it,
still no hope.
I installed VS 2005 pro and installed SQL server 2005 ent. The installer
only allwed me to install the workstation part because of my os. So i went
ahead and downloaded the developer version. I tried to uninstall the
enterprise edition first. while it was about half way completed the computer
suddenly turn off due to power failure. When i restarted the icon is already
gone from add/remove programs. So i installed sql2005 developer on top of
it. Everything was fine except for the documentation. Everything that uses
Microsoft Document Explorer ceased working.I had VS2003 on the same computer
as well. All i get is this

Microsoft Document Explorer cannot be shown because the specified help
collection 'ms-help://MS.MSDNQTR.v80.en' is invalid

I even reinstalled VS and Sql server serveral times. Still no use. The
installer must have crashed when it unregistering some assemblies (from what
i remember) somehow the ms-help got corrupted

someone had a similar problem, no solution
http://forums.microsoft.com/msdn/ShowPost.aspx?PostID=103780

Please help,

thank you

Howard.