Hi
Here's some info from the Dell Community on the topic:
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Re: Installing OpenManagement IT Assistant on desktop where default SQL server instance is 2008. Possible?
07 Jan 2009 12:08AM
Thanks for posting! Is your existing version of SQL a default instance or a named instance? If it is a default instance, you should install IT Assistant on a different system, since it has to use a default instance of SQL and putting the two together will result in corrupt data. If you are using a non-default instance of SQL, then the prerequisite checker will provide an error and a link to install SQL 2005 Express. Install that SQL, and ITA will install just fine.
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Hope that helps.