R help - Sep 2012 - Comparing x-intercepts between linear regression lines

Is anyone familiar with a way to test for differences in the x-intercepts (not
y-intercepts) of two simple linear regression lines in R? I'm familiar with
a method to calculate standard error estimates of the x-intercept
(http://www.mail-archive.com/r-help@r-project.org/msg50241.html), and ANCOVA,
which can test for differences in the y-intercepts. Any help would be much
appreciated.
Thanks,
Seth
 		 	   		  
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