light set up for a 30g

Errm, a 30x24x18 is ~ 55 gallons according to my calculations.

20 watts over a 55 gallons gives something like 0.37 wpg (watts per gallon) which is not enough for growing plants (forget Melon swords and Onions, you won't even be able to grow low light plants).

how can i get more wattage with out bring up the temp on my tank?

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You can always use a shop light or something from your local hardware store and use those instead. AFAIK, fluorescent tubes don't raise the temperature of the water that much...unless, and this leads me to my next point

i also have a none planted 20g and i put 2 40w reg bulbs and it's raising my temp from 76 to 80 degrees

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By two 40 w "reg bulbs" I hope you are not referring to incandescent bulbs. They are extremely inefficient, and should not be used in aquarium setups, as they lack the lighting intensity that is required for plants, and also generate much heat (as you have already noticed).

my 20 takes small screw in bulbs while my 30g takes 24 inch placement bulb

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You could always buy small screw in fluorescents for your 20 gallon. As for your 30 g (which is really a 55 gallon, I assume), I'm assuming that the hood only comes with room for a 24 inch T8/T12 tube (T8 = 1 inch diameter, T12 = 1.5 inch diameter). Obviously, this won't provide anywhere enough light for a 55g, especially if you plan to grow plants. The best strategy is to go to your local hardware store and purchase a shop light that can hold 4 tubes.

Screw-in compact fluorescent bulbs will provide a brighter, cooler light source for your 20g than incandescent bulbs. Look for something labeled 'daylight' if you can find it (I use Philips daylight bulbs). 'Warm white' bulbs will appear very red, and 'cool white' bulbs may make the tank look washed out.
Darkblade48 has the easiest, least expensive solution for your 30g (which really does sound like a 55g). You could also look into power compact fluorescent fixtures - either buy a complete fixture or retrofit your existing fixture with a kit from www.ahsupply.com. PC produces more light per watt and is great for planted tanks.