Hi Tim,
You might want to try it with the following:
par(usr=c(-2,1,ymin,ymax)
Where -2 and 1 are the exponents for your x-values, and ymin and ymax the margins you want for your y-values.
Then you plot as usual adding the following parameters:
plot(x,y,....,log="x",xlim=c(10^par("usr")[1:2]),xaxp=c(0.01,10,1))
Hope this will work for you!
It might also help to read through the help-files on "?par()" where all graphical parameters are explained.
/Birte