Video Quality.
 

I downloaded most of the ******** **** Season 1 as avi files. While they work and they play fine in Real Player or Windows Media player they are kind of blocky and pixelated as some parts.... but then the other half the time they are perfectly clear. Could this be my graphics card and not the file? I'm hoping it is.

It's the more complex images that are blocky.... so I was just wondering if there would be a way to fix this.

Could be due to a few things. The 1st & most likely is a poor conversion effort. Either due to lack of skills of the person who did it or due to cheap & nasty conversion codecs/program, or both.

Try VLC which has in-built codecs to see if it's due to a codec issue: http://www.videolan.org/vlc/ (choose nearest mirror site)