DLL to show message box

Hello, I have a custom indicator that shows an arrow in the chart when certain conditions are met.

I'd like my indicator to be linked to a custom DLL that shows a popup message box.

So what I'd like to do is the following:

1) to create a DLL with a function in it that when called by the indicator shows a popup message window (the actual message to be shown is simple static text).

2) to modify my indicator (I will provide the indicator) so that when the conditions are met it calls the DLL function that shows a popup message box (in addition to the arrow on the chart which is shown already).

I will provide the custom indicator and I'd like you to create the DLL file with the function required and I'd like back my indicator with clear comments about where and how it was modified to call the DLL function.

The DLL needs to work with MT4 on Windows 7 pro, 64-bit.