For reasons unknown to me the video quality of videos downloaded from the internet or internet streams is very poor on my computer on WMP or any other media player, the contrast is also higher than my normal display, any help?

Are you loading high quality videos?
If that's the case you most likely have the wrong codecs installed.
Check out www.matroska.org. Or install the VLC player, it's a player for almost any OS in existence, I believe, complete with the essential codecs (including Matroska, I think).

Hi!

Agree, you rather ought to uninstall you codecs completely and install any codec pack. I always advise K-lite Codec Pack - the most full one in mi opinion. In this way you won't worry about loosing any single codec.

is that all i have to install?
and how does it affect my speed?

Should be enough, I guess. If not you have to find out what codecs you need with a tool like G-Spot (nice name, that).
Your speed? Codecs shouldn't slow you down, they are only activated when you need them, not running in the background or something.