I've removed and named instance and tried to re-install an isntance with the same name on MSDE, but this doesn't work. Where in the registry is this info? and can I remove this from the registry to allow me to re-install the instance?
As far as registry value is concerned.. it is stored under the following path HKEY_LOCAL_MACHINE--> SOFTWARE--> Microsoft--> Microsoft SQL Server--> Instance Names --> SQL For clarity, post the error message you are getting.
To be fair do not play directl with the registry, as you may loose the SUPPORT from Microsoft (if any) for such unsupported tasks. It is a last resort you may consider if other options haven't worked out.