Crash Files
Bohemia Interactive has provided some helpful files when you experience a crash while playing or editing in Operation Flashpoint and Armed Assault.
Armed Assault
The arma.rpt, arma.bidmp and arma.mdmp files are located in your user\application\arma folder.
C:\Documents and Settings\username\Local Settings\Application Data\ArmA
Operation Flashpoint
Two files are created when OFP crashes, flashpoint.rpt and context.bin. These files are located in the root of the game directory and are only present if a crash is experienced.
The flashpoint.rpt contains information about which addons you have loaded, how much memory you have, which version you are running at the time of the crash. This can be a useful debugging tool if you are editing the mission files by hand, editing model configs. This file will often point to the cause of the crash.
The context.bin is a binary file and contains very little information to the end user.
DirectX
To better analyze the reason for malfunctions it might be useful to also create a DirectX diagnostic file.
To do this, hit the Windows "Start" button, and then select "Run...". In the dialog box that then comes up enter "dxdiag". After letting it finish (this will take a minute or so), click on "Save All Information", and specify a location of where the file should be created.
Sending Crash Files
Bohemia Interactive suggests that you email support@bistudio.com with those files, as it might help improve the stability of future patches.
Another option is to use the Unofficial Community Bug Tracker - report what led to a crash a attach the crash-dump files.