http://www.xe-team.de/index.php?site=articles&action=show&articlesID=8
you need the "SourceScheme.res" (if you don't have it extract it from "base source engine 2.gcf)
simply open the sourcescheme.res and look for the line "DefaultFixedOutline"
I changed it to something like this
"name" "Verdana"
"tall" "6"
"weight" "0"
"antialias" "1"
"dropshadow" "1"
edit it the way you like best :) there are also a lot of other parameters like
"underline" "overline" "antialias" "dropshadow" "yres" "italic" "additive" "blur" "scanlines