Okay...here is a preliminary product for you to test.
Download the attached .ZIP file, and upload the contents of the "upload" folder to your forum's root...this contains a set of images for the standard six sided die.
Once you have the images uploaded, and the .XML file imported, your users can then use something like:
[roll=1]5d6[/roll]
in their posts. The above will display five 6-sided die images (from the default defined image set), randomly generated.
If you have any questions about the use of this product (such as how to add more sets of images), please feel free to ask. If you have any suggestions for improvement, please let me know.