Howdy, henslee--
I'm not familiar with Grow Mulch, but based on a Google search it looks like it's a soil amendment that you put in the garden. So it's probably not intended for starting seeds.
The terms "potting soil" and "potting mix" are not reliable guides to what's in the bag, I've found.
I always use a "soilless mix" for starting vegetable and flower seeds. This is a store-bought blend of peat moss plus vermiculite or perlite. You can mix your own, but I'm too lazy. I avoid mixes with fertilizer (the seed and the growing medium contains all the food the seed needs for the first few weeks). I also don't use garden soil for starting seeds indoors--it's too compacted and there's a risk of soil-borne diseases.
Garden Web has some good info on starting seeds (and millions of other gardening topics). Hope that helps, and happy growing!
Hey, how about a Victory Garden for a Kerry win in November?!