On my local system I have developed an older site in asp.net 2.0 and do not wish to upgrade that site. However, I also want to build a new site and for that I want to use asp.net 3.5. Is there anything I should watch out for, or I can I just install the 3.5 runtime etc?
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Go ahead and install .net 3.5. It won't effect older projects. 

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The 3.5 framework is just extensions to the 2.0 framework, so in effect everything is 2.0 framework whether it uses any of the 3.5 stuff or not.
Jeff
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