are the 305 and 350 heads the same?, if not will the 350 heads give me some more power out of my 305 tbi?

What kind of car do you have? If its a H.O. engine it may already have 350 heads on it.
And as far as being the same, most of them are, i would look into getting vortec heads.

how do I know if I have an H.O. engine?

Let us know what year/type car you have. Post pictures of the engine. To receive you must give!

Also, I agree with the vortec head suggestion. They make pretty good power for their price.

S-D

I have a 1990 firebird formula 305 tbi, I don't have any pics yet

I think (you may want to search to confirm) that the 350 TBI heads may have slightly larger valves in them, so you may see minor gains with that swap (or not). I wouldn't count on much with either the 305 or 350 as both are regrettably lame.
If you are going go through the work of changing heads, I'd consider vortecs.
S-D