Decent codecs: http://www.divx-digest.com/software/nimo_pack.html

Also have another backup player as well (as well as divx player) called VLC & is free & has built-in codecs & plays all but the odd wmv file: http://www.videolan.org/vlc/ (choose the nearest mirror site.)

VLC is not the prettiest of players & its controls are a bit flimsy but it plays most things & that's the important thing!