is it illegal to post youtube links?

Nope, it is Youtube's responsibility to maintain the legitimacy of their content. You can even embed Youtube videos in your posts with the bbcode I created:

http://www.guba.com/watch/2000942545 (!)

http://sjc-v90.sjc.youtube.com/get_video?v..._id=H6PAhow2BJQ
http://chi-v47.chi.youtube.com/get_video?v..._id=T1Hb8l09hks
http://ash-v14.ash.youtube.com/get_video?v..._id=ZA92UnvcppU
http://sjl-v146.sjl.youtube.com/get_video?..._id=hE5-VfUXtyE
http://ash-v16.ash.youtube.com/get_video?v..._id=Gx8wUDkG-Qo
http://lax-v107.lax.youtube.com/get_video?..._id=Rxg2SJodDR0
http://lax-v14.lax.youtube.com/get_video?v..._id=HFzitJzlwYQ
http://ash-v37.ash.youtube.com/get_video?v..._id=WCuof6-3k5k
http://ash-v43.ash.youtube.com/get_video?v..._id=elKg4UOv0gg
http://sjl-v142.sjl.youtube.com/get_video?..._id=6hI5lRK5zx0
http://lax-v220.lax.youtube.com/get_video?..._id=CqzUpUt2sPg
http://sjc-v59.sjc.youtube.com/get_video?v..._id=IjFJsz1CZe8
http://lax-v85.lax.youtube.com/get_video?v..._id=CdBenKytAfw
http://ash-v9.ash.youtube.com/get_video?video_id=kzFjqgErwa4
http://lax-v5.lax.youtube.com/get_video?video_id=dBYBTupFmGw
http://ash-v59.ash.youtube.com/get_video?v..._id=JWtlydhIbZQ
http://lax-v257.lax.youtube.com/get_video?..._id=SDYhrPW3KX4
http://ash-v172.ash.youtube.com/get_video?..._id=3hQiCh9WoS4
http://cache.googlevideo.com/get_video?vid...ash.youtube.com
http://sjc-v8.sjc.youtube.com/get_video?video_id=zj-TzM46L2c
http://sjc-v178.sjc.youtube.com/get_video?..._id=s7U1jSiXBvA
http://sjc-v74.sjc.youtube.com/get_video?v..._id=hJTJSlJO0uk
http://ash-v73.ash.youtube.com/get_video?v..._id=iEPSGSn-Dp4
http://chi-v230.chi.youtube.com/get_video?..._id=eDwESq1ZGcs
http://ash-v109.ash.youtube.com/get_video?..._id=gd9kLtzZuqo
http://ash-v207.ash.youtube.com/get_video?..._id=hqcUvpAvGjc
http://ash-v70.ash.youtube.com/get_video?v..._id=8u63blEE4bo
http://ash-v116.ash.youtube.com/get_video?..._id=9Cz2tM-Dex8
http://ash-v298.ash.youtube.com/get_video?..._id=DfFwec4O1Lg
http://chi-v303.chi.youtube.com/get_video?..._id=QgQYpdfjuSU
http://chi-v42.chi.youtube.com/get_video?v..._id=YzsYDs21VWc
http://ash-v190.ash.youtube.com/get_video?..._id=Sn9nIWzOoUM
http://lax-v111.lax.youtube.com/get_video?..._id=QlX2tnUAf2E
http://lax-v224.lax.youtube.com/get_video?..._id=9AOl_AjvmXI
http://sjl-v150.sjl.youtube.com/get_video?..._id=TsSXVPdJUHk
http://ash-v233.ash.youtube.com/get_video?..._id=PQEQADnSg5M

How do you get those videos to play? Which player do you need?

Download and rename the file to anything with FLV extention, example video.flv
If you don't have already a player to play it, download a good one here: http://www.free-codecs.com/K_Lite_Codec_Pack_download.htm

Oh damn, I forgot about this, though even if I hadn't I wouldn't be able to watch it since I'm not home, but will try it when I am. Thanks Max.