Skiddish dog wont walk on leash

Question
I have a 5 year old purebred rat terrier.  She is the sweetest dog I've ever met.  
She loves my kids dearly and would do anything to protect them.  The
problem is that she seems to be lacking in the brains department.  The dog is
very skiddish.  She seems to be afraid of EVERYTHING!  I live in an apartment
and it is mandatory that the dogs are on a leash when they are outside.  It
has become very difficult living with her because I cannot get her to go to the
bathroom on the leash.  I cant' even get her to move on the leash.  She
freezes up and will not move.  If she does move she attacks the leash.  This is
so disappointing because my other dog is very well leash trained and will go
for walks with no problem.  I would love to be able to take both dogs for a
walk but right now the most important thing to me is just getting her to go to
the bathroom on the leash.  I am DESPERATE.  If anyone has any tips PLEASE
let me know!!  This is seriously affecting the relationship I have with my dog
and if she doesn't accept the leash I have to decide between my home and my
dog.  The apartment manager just asked me to put her on a leash yesterday
so it's been noticed... the clock is ticking.

Answer
My advice would be to enlist the advice of a good clicker trainer (www.clickerteachers.net).  If the dog is food motivated, you can learn to acclimate her to the leash first, then to walking with it on, then to going potty with it on.  
Use treats that are better than she normally gets.
Start in a quiet location where she isn't normally nervous.
Entice her to accept the leash by feeding her a bit of peanut butter while you clip it on.  Then, take it right off.  Play "open bar" and "closed bar".  The leash goes on, the peanut butter flows... Leash comes off, dog gets nothing.  The object is for her to want to put her leash on because it pays off!  Outdoors, try the peanut butter, but have some roast beef in reserve!