Trishka,
Above advice is correct - provided your 1st provisional licence hasn't expired by 5 or more years ago you will be fine. Simply apply for a new licence in the normal way, with the appropriate fee and your last licence with your application. Forms are available from your local Garda station or your local Motor Tax office.
Provisional drivers whose licences have expired 5 or more years have to complete a Driver Theory Test, before they can obtain another provisional.
If someone is on their 2nd provisional licence, they must apply for their driving test before a new provisional will be issued.
Full licences are issued for varying periods, depending on your age. For most people with full, 10 year licences, if your licence has lapsed for 10 years you have to do a driver theory test, apply for a provisional and undergo your driving test again.
On a final note, Car drivers (Cateogry B) are not required to be accompanied by and under the supervision of a person with a current full driving licence to drive, where they are on a 2nd provisional licence. Further info is available on the Department of Transport website here: http://www.transport.ie/viewitem.asp?id=2970&lang=ENG&loc=1233 (http://www.transport.ie/viewitem.asp?id=2970&lang=ENG&loc=1233)