Solids are anything other than milk and water. Amelie didn't get any teeth until she was 10 months old and we weaned at 5 months, and we did a mixture of finger foods and puree early on (so she was munching toast and things like cucumber and peppers quite easily with no teeth).
Start with one meal a day (which you're doing with his rice cereal). Then after a few weeks or whenever you feel he's ready, introduce a veg puree (sweet potato is a good one to start with, you can add formula or EBM to it to make it the right consistancy). When you're on 2 meals I'd do his cereal at breakfast and veg in the early evening for 'tea' (5pm or so).
HTH
