I have a letter from my boss stating that i will be paid a salary of at lease 500.00 per week. What if my paychecks arent even close to that?

Salaries, pay, etc. may be changed at will by employers unless there is a written employment contract *for a definite period* (e.g. a one-year contract) which guarantees or locks-in the salary for that time; therefore, your employer can say they'll pay you X then instead pay you Y.
The above said, you *may* have a legal claim if all of the following criteria were met:
1) The employer promised you something (e.g. a certain salary) to get you to do something (take a job);
2) In order to do that thing (take the job), you'd have to do something significantly detrimenal, such as giving up an existing job or relocating;
3) The employer knew that you'd have to do that detrimental thing (relocate or leave an existing job);
4) Despite knowing that you'd have to do that detrimental thing, the employer still made the promise to induce, or cause you, to take the new job; and
5) It was reasonable for you to rely on the promise--there were no warning signs or reasons to doubt it.
If ALL these criteria were met, you may be able to enforce the promise, or at least get some compensation, in court (by suing) under the theory of "promisssory estoppel." The hurdles for you in trying to make out this claim, however, will be--
a) You must have given up an existing job or relocated; if you were unemployed at the time and didn't move, you did nothing to your detriment;
b) The employer must have known you'd have to give up a job or relocate; 
c) It may be very hard to prove that it was reasonable for you to rely on (or count on) the promise, because a promise to pay you a certain amount for a job which does not even state the hours is not very credible.