I'm just curious have you tyred removing -window -vidmode 640,480,60 and running halo in normal full screen with lets say a resolution of 1600-900 or any of the other resolution modes to see if the text works in full screen mode. Reason i say this is because the -window is part of the original developer comands and is not a normal user setting and was not intended to be used by the home user its why the window option is missing from the vid settings in halo. It was only later found out and made public by users however I remember them saying that it may not work correctly for everyone and may result in undesirable behavior.
So if you where to test in full screen and test all the resolution settings and you are able to see the text then it maby that your comp simply does not like windowed mode