Yea, just look into the ability Larva>Morph unit and check your units requirements to "HAve Lair" like Ahli said.
And on the other note... Dude, you play on such a shitty graphic, how can you stand this?....
My sympathies mate... I had the same prob when sc2 came out. So I went on and won a strongman competition and I bought myself a new beast-pc. Sc2 is so awesome on ultra, I sincerely wish you to be able to play sc2 on ultra in the future. Its unfair... Dudes who are mappers or modders should be able to play the game on ultra.
SC2 is not a very graphics intensive game. You can pick up a graphics card that can easily play the game on high @ 60fps for $80 or so. IMO, if you don't have the money/need for a nice gaming computer, at least get a computer that can handle that.