Depends what type of glitches they are. Generally overheating ends up with newer machines shutting down (most PII and higher machines detect the CPU temperature) and if it gets too high it either starts playing a song through the PC speaker to alert you to shut it down, or eventually shuts itself down. Other symptoms of a video card overheating can be video going black or sometimes getting a plaid type of coloring (can also be bad video ram though).
Check the fans on your video card and CPU heat sync to make sure those are spinning ok. You can also sometimes make sure the heat sync is on correctly as the chip can overheat quickly without it.
As for a check, the lame thing friends and I've done are take off the side of the system and set up a fan to blow on it. If the same error occurs, unless it's a bad heat sync or bad heat sync fan on your video card or CPU it's probably not heat related.