Windows will naturally handle most formats. For some additional formats, I use Shark007.net - Windows 7 Codecs they don't install any players, just the codecs.
Home LAN through Linksys hub to 4 port and wireless switch/router. Networked HP 2600n. Wife's computer running Windows 7, and spare laptop running Ubuntu "Karmic Kola" (9.10).
Everybody has their favorite codec packs, and after trying out Shark's I moved over from K-Lite. Others like VLC <shrug> Pick the one that looks best to you.
Home LAN through Linksys hub to 4 port and wireless switch/router. Networked HP 2600n. Wife's computer running Windows 7, and spare laptop running Ubuntu "Karmic Kola" (9.10).