A am building an IR receiver based on the simple circuit from http://www.lirc.org/receivers.html
I want to drop out the '78L05, 100mA, voltage regulator' and use +5v from USB instead, but I am not great with electronics...

Can someone please advise me of what a suitable value for R1 (pulldown resistor) would be?
Also, would I be safe to remove D1, as there will be no risk of negative voltage?
Would there be any other part of the Circuit that would need to change for it to work properly?

Zacc D