most of them are located in the $windows$ and $system32$ directories, and are txt files... the do NOT take up that much space and i would not recomend messing with them if you do not know what you are doing.
good luck
~KB
edit**
keep in mind that some of these .log and .txt files are refrenced for system operations such as windows updates, and removing them or editing them without a working knowlege of what they do, what dependencies they have could cause more problems than it's worth... just thought i'd pass that along.