ISINTEG (Information Store Integrity checker) is a useful and potentially dangerous tool for checking the integrity of an Information Store and fixing it (the potentially hazardous part).
Much like its cousin ESEUTIL you have to run it from the /bin directory of the c:\Program Files\exchsrvr directory as it is not added to the PATH system variable by default.
The easiest and safest option with ISINTEG is -test. Also don't forget to use -s [SERVERNAME] as this will tell ISINTEG what server to run the test on.
There are other flags that ISINTEG can use such as -patch, -verbose, and -l [LogFile]. But the one that you should be especially careful of is -fix. This has been know to kill an Exchange server, so make sure you have a back up of you Information Store before running this, as a bad store is still better than a bad installation of Exchange. You have been warned!