Check if file excists

hi there.

in php there is a function if_file_excists

Is there something like that in actionscript?

In a content management system i build people can upload images or small swf’s

so i like to check if they uploaded the image load the image otherwise load the swf

i add a loadMovie script wich loadsthe excisting file into movieclip and getting the data from a xml file

is this possible (the if file excist part)

Thanx