pic16f684 programmer
JDM blows chunks!!!! It is notoriously unreliable with ALL software - especially with newer PC's. The serial ports sometimes don't supply enough voltage for JDM to work properly. I would suggest this programmer:
ht*p://www.sprut.de/electronic/pic/projekte/brenner8/index.htm#aufbau
The website is in German, but easy to navigate. I recommend the Brenner8-P. The version I built is rev 2. The current version is Rev 4.
This is an excellent USB programmer. It programs pretty much all of the 5v PIC's, and is fast. However, you must use their software (which is very good).
Or you could also use a parallel-port based programmer (such as Tait). They are just as simple, and much more reliable.
If you insist on JDM, use schottky diodes. They have a lower voltage drop (the less that drops across the diodes, the more there is for Vpp). Also, keep the cable as short as possible. Or, better yet, use a layout that allows you to plug the programmer directly into the serial port with no cable.