Dear lre1954 , Your Imac model No. A1144 doesn't acquire enough RAM required for Leopard OS. As Andrew has mentioned that leopard demands minimum of 1 GB RAM . So, you must check for the specifications first. All the best.

The main reason behind the slow behavior of macbook is the accumulation of unused data. Cleaning the Mac drive can clean the problem too. You can use mac utilities like Stellar Speed up Mac to remove all types of unused files and to remove unused mac applications.