I've had problems in SWKS 2003 (with certain files) when attempting to modify the "custom" settings for the "deviation" and "angular" tolerances for STL export.
No matter how they are set, the resultant output file is the same exceptionally LARGE size.
SolidWorks 2004 (even during Pre-Release) has avoided this problem, so I've opened up files with the new version sometimes JUST to perform the STL conversions.
The problem in 2003 is as if the angular tolerance is "stuck" at a setting of around "1" degree.
This results in an output file which is roughly 30 times the size of one created with a looser tolerance of 15 degrees, for example.
The higher precision comes with a cost in data overhead, so don't make the polygon meshes any finer than you really need.
You may need to experiment with various custom settings in 2003 to see if your installation is plagued at times with the same "frozen" mesh density problem I've been seeing.
I should mention that I almost always make use of the STL preview during export.
Per O. Hoel