Since MediaFire (and photobucket) insist on resizing my image, I gzip'ed it instead. Winrar and similar for windows should hopefully be able to extract it.
New link: http://www.mediafire.com/file/2weve835zy74x5s/Ultrasonic%20sensor%201.png.gz
Ok so I got the transmitter working( I can hear it clicking)
You have an exceedingly good hearing?
Anyway, to get this pretty simple and unstable(?) circuit working, you should have a (oscillo)scope and watch it with, while you adjust RV1. Lacking that, perhaps skipping one stage will help, maybe even two, with a reduced range of course. But it might get you started. As well as experimenting with RV1, as its just as a simple threshold adjustment. Pretty much just something I cobbled up without too much thought.
Also, as previously stated, AlphaZeta's solution is really much better!http://www.kerrywong.com/2011/01/22/a-sensitive-diy-ultrasonic-range-sensor/
Except something I just noticed; about his note about using higher voltage to drive the transmitter. Do not do that with that bridge circuit (essentially the same as mine), as the arduino output has 5V (if its a 5V arduino, of course). You'd have to change it somewhat then, an additional inverting stage would be needed to shield the arduino output from higher voltages.