Programming a microcontroller with another microcontroller
There are several open source PIC programmers that will program the PIC24FJ256GB106.  The gotcha is all of these are based on a PIC18, none seem to use a PIC24 to do the programming.  Of course since the schematics and firmware are provided, if you are set on using the same PIC24 to do the programming, you could convert one of these boards (and the firmware) over to that chip.

Here are three:

Olin Lathrop's LProg, which you can buy from Microchip DIRECT for $20.   Here is the schematic and here is a link to the firmware.  This is the one I recommend.

DIY PIC Programmer.  You can buy it for €20 here.  Firmware available here.

usbpicprog. Looks like you have to make your own board for this one.  Schematic available here, firmware here.