I can't find System.speech

Click on Project in the menu bar then click on Add Reference. Click on the .NET tab in the window that appears. Search and select System.Speech. Click OK. It should work after that.

Check the reference assemblies directory typically found in : C:\Program Files\Reference Assemblies\Microsoft\Framework\v3.0\

That should have a copy of System.Speech dll

Check your project type, and the version of the framework it's targeting.

SpeechSynthesizer exists in .NET 3.0, 3.5 and 4 - but only in v4 of the client profile. If your project targets anything else, that would explain why you're not seeing it. Otherwise, it should be there though...