Help!! We have a sun room that is perfect for growing tomatoes during the cold months. However, just about time the fruit is beginning to produce we get an influx of spider mites that ruin the plants. How do we prevent and how do we get rid of the spider mites? Any help is certainly appreciated!

Spray with a seaweed solution and those pests will be gone. Maxicrop is the first that comes to mind, but there are others...
Make sure you spray the undersides of the leaves and do not spray it if it is real hot. The heat factor should not be a problem for the next few weeks.

for an Organic treatment try no spider mites its good stuff
http://www.nospidermites.com/

I'd be really cautious about a product recommended that promotes itself as organic but doesn't give a view (that I can find) of the label or active ingredients. There is no way to evaluate what is in the product, and that sends up a red flag for me.

Get the tomatoes outside! Spray weekly with seaweed.