Hi Mark
Microsoft is the maker of SQL Express and if you experience an issue installing or configuring or using SQL Express, dorefer to the Microsoft Support for SQL Express
A good starting point is http://www.microsoft.com/sql/editions/express/support.mspx
Other Microsoft support topics:
http://support.microsoft.com/kb/307288/en-us
A couple of things found while searching through the Microsoft Support area:
You want to ensure that you have all the latest Windows service patches on this computer, and then perform the installation again.
You do need Microsoft .NET 2 with any service patches installed prior to installing SQL Express 2005
If you previously had a beta version of SQL Express installed - that must have been completely removed before installing SQL Express 2005
You must be logged in with full rights to the computer when installing.
I would also suggest performing searches on the internet for any error messages you receive, including your operating system etc to help you narrow down why this is occurring on your computer.
- Joyce