I think you should make a phone call to some place like this and get the appropriate information.
http://www.3riversarchery.com/Index.asp
I may be wrong because I know nothing about bow building but you can either make a laminated bow or a selfbow if the log is big enough. You also might want to slice the end of the log to show the end grain with a ruler against it to show the size of ring growth. You may find this interesting.
http://www.huntingnet.com/forum/tm.aspx?m=2770248