Hi Thomaska
The amount you'll be given depends on where in the country you are living and your family circumstances. A single person in Dublin must look for a property of no more than 400 euro per month. If you have a child, no more than 1000 euro per month, and two or more children, no more than 1200 per month. If you have a partner living with you who works full time, you wont' qualify if they are working full time regardless of the fact that you are on disability.
Rent allowance is paid by the community welfare officer of your local health centre. Sometimes they can be flexible with rent ceilings if rents in the area are above the general ceilings. If you've never seen your local CWO you'll need to ring and find out what their clinic times are, as they are gnerally only available to the public at specific times. You'll probab;y need your PPS number and some ID. You will also need to be registered on the local authority housing list (so ring them for an application form). The CWO will give you a form to fill in which will have to be signed by the new landlord to confirm the rent (if its above the ceiling, the CWO will refuse to pay towards it). The form will need to be stamped by the local authority to confirm you are on the housing list and then returned to the CWO.
In relation to the deposit, some CWO's will help with the deposit, others wont, again it can depend on your circumstances. One of the probs with rent allowance is the CWOs pay rent in arrears and landlords more often than not want it in advance each month.
Hope this helps!