Sperm is dead the second its dry right?
How long does it to take to die and can it be sped up with a hair dryer or such.

Yes, sperm is dead when it is dry- but you have to be sure all the sperm is dead- even the stuff inside her vagina or inside his urethra - all of it.

Usually about 4 hours is safe.
Susan

And please, for heaven's sake, don't blast anyone's genitals with a hair dryer! (wince)
If in doubt you could always use spermicidal jelly, or condoms with spermicide. You can get those at any decent drugstore.