I have a ProntoNEO and have most of the lights in my house on X10 switches. You need to get an IR receiver for X10, such as the IR543. This is what I have. The IR543 only lets you control one set of unit codes at a time, so you can only control up to 16 devices unless you change a setting on the IR543. There may be a newer version of an IR receiver that lets you control all house codes and all unit codes at once. Check X10's site for it, or google for X10 and infrared receivers. I remember seeing a site that modified the IR543 to accept all house codes and sold their version for around $100.

To get the IR codes into the NEO, you can download a setup file from this site. That is how I got my NEO working with my IR543. Search the files section of remotecentral.com for X10 and the NEO.