An Installable Interrupt Service Routine ISR is an interrupt routine with a shorter latency than an IST.
For more information see the Win CE help for example: http://msdn.microsoft.com/en-us/library/ms836807.aspx
We can provide sample code were you can see how to use an ISR. See: [Article not found #100631]
If you use Visual Studio instead of embedded Visual Studio you have to change some project settings to get an running ISR DLL.
In VS 05 go to Project-> Properties-> Configuration Properties-> C/C++-> Code Generation-> Buffer Security Check set this flag to "No".