Dynamically Switching Databases In A Script

I've got a situation where I need to execute portions of a script against every database on a given instance. I don't know the name of all the databases beforehand so I need to scroll through them all and call the "use" command appropriately.

I need the correct syntax, the following won't work:

DECLARE DBS CURSOR FOR
SELECT dbname
FROM #helpdb
ORDER BY dbname

OPEN DBS

FETCH NEXT
FROM DBS
INTO
@dbname

WHILE @@FETCH_STATUS = 0
BEGIN

USE @dbname

The last line - the "USE" statement - is invalid. The following for example works:

USE master

But when supplied a declared variable a syntax error results for the use command because it expects an identifier.

So .. what is the correct syntax to pass a declared parameter to "USE", or is there another way to meet this requirement?

Thanks for your time.