The problem is, the DM doesn't like rolling fights - most of her adventures can be solved through clever thinking, reasoning with NPCs and out-of-combat magic use. This is quite satisfying most of the time and I do like it. However, as the result, my wizard is much better suited to espionage than to actually hurting things.
Actually, this might work more to your advantage than not, a lower level fight against a dragon often requires great preperation and strategic thinking, and having an open minded DM like that is certainly a preference. The first thing you want to do is limit the dragon's mobility, fighting it in its lair is often preferable to fighting it outdoors where it can make use of an open sky, if it does turn out that fighting it in an enclosed space is going to be impossible, there are a few things you might try.
It depends on the size and age of the dragon in question, but it's entirely possible that you might get lucky and get an Earthbind spell (Draconomicon) through its SR, and even if it makes its Fortitude save it'll still have its flight speed greatly reduced. On a similar note, both Scale Weakening and Suppress Breath Weapon from the same book are excellent spells when dealing with a dragon with a SR you can actually beat.
As for your other spells, both Vampiric Touch and Bestow Curse are sort of pointless, considering you'd need to get close enough to touch the damn thing, Troll Form is pretty powerful normally, but a lack of a ranged attack and negation of Regeneration due to its Acid breath weapon makes it somewhat useless. Summon Monster IV however does offer a number of excellent choices, as a group of smaller flying creatures can really become a pain for a larger dragon very fast. Consider summoning a Lantern Archon or two, they have Perfect flight speed, a ranged TOUCH attack (Though it doesn't deal much damage) as well as Magic Circle Against Evil and Teleport at Will. The Archon can't actually bring another creature along with it, but it can bring 50 pounds of items, such as 12 tanglefoot bags, dropped from a height above the dragon capable of dealing enough 'damage' to the bags for them to split open and spill their goo all over it, and even if the rule states that Huge and larger creatures aren't affected by them, try to reason with your DM that the amount of sticky substance would at the very least hamper its movement. Aside from that, the Celestial Giant Eagle is an excellent aerial summon in that level of Summon Monster, and even if their attacks won't make it through the dragon's AC all that often, they do have better mobility than the dragon, as well as Evasion and a decent Reflex save to soak up its breath weapons.
If you do manage to ground the dragon, summoning a couple of Howlers can quickly make life hell for it if it fails its Reflex save just once against their Quills.
In the end, the greatest weapon you have against a dragon is preperation, make sure you have every advantage you can get, Energy Resistance spells will do wonders, and getting a method of flight for your melee warriors is a must if you can't get the dragon grounded. Heck, getting your hands on a ballista or two and preparing them in advance would be great, maybe a pair of them with a large net to take the dragon out of the sky.
