I have SQL 2008 R2 on my computer and it works fine with the database. If I install Visual Web Developer 2010 express it says I have to install SQL Express , per it is a dependency. I would prefer to only install web developer.
Will an express installation effect my current installation's operation at all?
On
Officially, they can coexist.
Unofficially, my experience with a joint installation is painful. SQL Server patches would fail mysteriously on machines with a joint install. Sometimes you could find fix information in a KB article, sometimes not. Sometimes reinstalling SQL Server worked, sometimes an OS reinstall was required.
You can take the risk on a development server, but I wouldn't do this in production.
Yes they can coexist as they will be installed as separate services - see this forum post