Tomato seeds are actually quite easy to save. It takes a couple of days and it smells terrible, but its worth while.
 

• Let  your open pollinated or heirloom tomato fully ripen on the vine before picking it.
• Cut the tomato in half and squeeze out all the gel and seeds into a jar or bowl.
• Add some water, stir it up and let it sit for several days.
• When it starts to ferment, you'll see bubbles in the mixture and possibly mold on the surface.
• Add more water, stir, and pour into a strainer. Rinse well.
• Put the seeds back in a jar or bowl and add water. Discard any seeds that float.
• Pour the water off and put the seeds in a bowl or on a fine screen to dry. Place in a cool dry place.
• After the seeds are fully dry, put them in envelopes and label them with the variety.
• In a cool and fairly dry place, tomato seeds should last at least three years or more.

• Seeds from hybrid plants in most cases do not grow true. Meaning that the plants you get most likely will be different from the the parent plants. Hybrids are the combinations of different varieties of plants. When you cross pollinate two tomato plants of different varieties, you get a plant different from both parent plants. However, the seeds from the resulting plant may be wildly variant from both the parent and the grandparent.