Vermiculite is a soil texture amendment. It makes the soil more crumbly and light, but not as good for drainage as perlite (the white stuff).
Look on the back of the potting mix and there should be NPK numbers somewhere. Potting mix with some extra vermiculite or perlite isn't actually a bad way to go.
If your garden store has promix, that's another pretty simple medium to work with, but if you are using it, read the 'why i should re-pot' thread in the FAQs first! Actually, read it anyway- it applies to any indoor soil grow.
You can use the 'organic' pottng soil later when the plants have 5 sets of leaves. Again, extra perlite is good.