Above link may also be useful to you. I gave it a half-asssed shot and couldn't get the flashing down, but I did not have the "exact" parts he suggests.
I did have success in buying a single flashing LED and wiring it up to a bunch of other, non-flashing LEDs and that did work. I felt it lost much of it's intensity, however, when it was all hooked up. Used it for a year then bought Hyperlites, which do what I've been trying to acheive all the time.