There are several vintage sewing machine groups on Yahoo! Here is a link to Treadleon (the name of one of the groups, I think the one that specializes in White machines):
http://www.treadleon.net/
If you can figure out the model number of your machine (try Googling "images" for White treadle sewing machine to look for a photo similar to your machine, then click on the picture to find out the website that may list the model #), this site has free threading diagrams:
http://www.sewusa.com/Sewing_Machine...g_Diagrams.htm