If so, why not enter Circalit's competition - write a 3-5 minute comedy sketch, and the prize is to have it produced by an award-winning producer.
(If you think you can't write a script, why not dig out one of your humorous stories and try converting that. Plenty of tips here on how to write a screenplay.)
If scripts don't appeal in any way, it's still worth having a look at the Circalit competition pages - they are running a wide variety of comps at the moment, from pitching a feature film to 500-word flash fiction comps. Some of the comps are even free to enter!
Edited 23/11/11 - also look at BBC Writersroom for tips on script-writing.