Did you follow all the steps in the VSTO deployment walkthrough at http://msdn2.microsoft.com/en-us/library/bb332051.aspx?
You pretty much have to follow that step by step to get a VSTO deployment to work.
What you have to do is set the security on the project assemblies, VSTO requires FullTrust to run. If you have that set in the CASPOL, all the requirements and pre-requisites installed (Framework, VSTO runtime, possibly the VSTO language pack, required PIA's, any other dependencies, possibly KB 908002, etc.), strong naming and so on then things should work.
When you start Outlook if you look at the COM Add-Ins dialog (Tools, Options, Other tab, Advanced Options button, COM Add-Ins button) is the addin listed? Is it checked? When you select it are any errors indicated? What about looking in Help, About Microsoft Office Outlook, Disabled Items button? Is the addin disabled?
What do you see if you look in the Framework 2.0 configuration utility? Do you see FullTrust granted to your addin assemblies?
If all that is done correctly the only other thing that would disable your addin would be unhandled errors. Any addin must handle all errors or risk getting disabled by Outlook.