It is not uncommon to download and install something and have it not add a launcher in the GUI menu system. Best thing to do at this point is to try running it from command line, i.e. '$ xawtv'. Hopefully it'll be in your environment path, otherwise, you'll have to use full path and file name, e.g. '$ /usr/bin/xawtv'
If you continue to have problems finding it, then can try command like 'slocate xawtv' to try and get the system to show you it's location. Might be who of you to research the xawtv home page: http://linux.bytesex.org/xawtv/
Once you sort out how to start it from command line, then can add it to the GUI menu or (depending on the windows manager) make a desktop launch icon.