Codecs installed on your PC may be divided on supplied with OS and installed by you with some Video Players and Codec Packs. I wouldn't advice to remove Codecs supplied with OS, but they can be selectively deactivated in WinXP via Control Panel - Sound and Audio Devices - Hardware - Audio & Video Codecs.
Codecs installed by you, can be safely removed:
a) uninstall Codec Packs and Players that installed extra Codecs via Control Panel - Add & Remove Programs;
b) Download and install
Graphedit to see remaining Codecs List via its Menu;
c) Download and install
DirectShow Filter Manager. Delete Codecs from the List of filters it compiles on your PC. Look in GraphEdit, if anything left;
d) Run regsvr32 quartz.dll to repair standard OS codec links in your system;
e) DONE
In Win7 you may want to use similar OS features to deactivate and delete Codecs, and then clean the rest with
Win7DSFilterTweaker instead of DirectShow Filter Manager.
Once you uninstalled all extra codecs, it may be a good idea to consider installing latest
HD Pack to support quality sat channels playback via your Sat Viewer.
Have fun...