I ran both those sites through ScanURL.net and here are the results:
Watch-Movies.net -- http://ScanURL.net/?u=Watch-Movies.net#results
Xvid.org -- http://ScanURL.net/?u=Xvid.org#results
Both sites are reported safe (no malware or phishing). Also, reputation/trust ratings are pretty darn high for each, with many votes. So, should be safe from a user/reputation standpoint.
I like Nosher's recommendation, though - get your codec from the source, just to be sure.