In trying to watch some anime, I've come across resolution woes. My video program of choice is Zoom Player, which does install on my 64-bit Ultimate system. That said, it and other non-WMP programs that I try to use to watch videos render pixelated images (my fallback form ZP is VLC Player, and it too has the problem). So I was fine watching .avi files on WMP until I was unable to get WMP to render .mkv files, despite the fact that I installed the .mkv codec pack. Does anyone know of a good video program without rendering issues, or a fixed version of Zoom Player? I'd appreciate the info.

Yes use the Vista Codec Pack, remove any other codec programs as these packs contain every codec you will need, They also have two versions and you will need both for Vista X64.
Included in these packs is a player called Media Player Classic which is capable of playing .mkv files.
To adjust the hight and width of movies in MPClassic use your keypad keys 2,4,6 and 8.

Vista Codec Package Homepage

Thanks for the link, dmex, though that site isn't exactly navigable. Anywho, I can render my videos now, so things are A-OK.