as far as i kno u cant, i think its hard coded to allow the game to start up proper before any particles start
I think theres a program sumwhere with allows u to view particle systems out side of hl tho, never downloaded it so i wudnt kno where to get it from, im sure someone else will be able to tell u tho
/edit - was looking for particle information myself and stumbled across the program u need
NSPEdit