I don't know if it is this what you are exactly asking, but here:
void SetupLoadScreen(string&asTextCat, string&asTextEntry, int alRandomNum, string&asImageFile);
Determines which loading screen will be shown when changing maps.
asTextCat - the category of the loading text in the .lang file to be shown on the loading screen
asTextEntry - the entry in the .lang file
alRandomNum - if greater 1, then it will randomize between 1 and alRandom for each LoadScreen giving entry the suffix XX (eg 01). If < =1 then no suffix is added
asImageFile - the image to be shown (optional)
From here:
http://wiki.frictionalgames.com/hpl2/amn..._functions