I'm not 100% on this, but I don't think the SSMS will install if 2005 SSMS is already on the machine. I believe, you need to uninstall 2005 SSMS and then reinstall 2008 to get the client tools to appear.
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If you follow the direction given HERE[/url] you'll likely increase the number and quality of responses you get to your question.
Jason L. Selburg