If you're feeling brave, have a look at
http://www.dd-wrt.com/dd-wrtv2/index.php
It allows blocking by any combination of service (including MSN), PC, time, website and keywords. It does require flashing the router though and will invalidate any warranty you have
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Sorry, just noticed you have the WRV, don't know if that is supported, I have the WRT. Sorry.