Note: GPU mining is strongly discouraged at this point (see here), as it is both unprofitable and hard to set up correctly.
This page will provide you with a script to get you started with Litecoin mining. Remember that Litecoin mining is very different from Bitcoin mining, and usually requires much more tweaking to get optimal results.
Instructions: Download the above script and put it in the same folder as your miner's executable, then run it (the script you just downloaded, not the miner's executable) from there.
Important: In most cases, fine tuning is necessary to get the best results for a particular system. To get your miner to run stable (with no hardware errors), you may need to tweak the thread concurrency and intensity settings. Please read the documentation for more information. You may find some sample configurations for your card on the Litecoin Wiki.
Important: If switching from Bitcoin mining, make sure your GPU memory is not too underclocked!. In general, the memory clock speed needs to be higher than that of the GPU engine.