SQL Exp 2008 needs dot net 2.0 sp2 but I have dot net 2.0 ..

When I tried to install it I got the error message :
---------------------------
Microsoft SQL Server 2008 Setup
---------------------------
SQL Server 2008 Setup requires Microsoft .NET Framework 2.0 SP2 to be
installed.



Download and install .NET Framework from http://www.microsoft.com/net/ and
then rerun Setup.
---------------------------
OK
---------------------------
But when I download and install SLQ 2008 Express and install it I get the
message "this is already part of your Operating system". I thought maybe it
is the wrong SP. But Windows update says everything is up to date. And
when I check the Uninstall list it says I have dot net 2.0 sp2.
Any ideas?
Thanks,