Well the main difference between meditation and sleeping is that meditation is a state of super consciousness while sleeping is a state of sub consciousness.
But you may say that we get refreshed after a long deep sleep and like wise after meditation. (Here what i mean by getting refreshed is increase in the degree of alertness and increase in the performance of our intellect) . This is because our body the greatest machine ever gets itself repaired and reset as we aren't giving any work to it or forcing it . But the main difference between sleeping and meditation is we spiritually travel towards a blissful state of ultimate or GOD consciousness as stated in Pathanjali's Yoga Sutra the source book of the science of Yoga and Meditation. This is the ultimate state of bliss or being the GOD. But on contrary sleeping is something like shutting yourself in a sound proof room in order to escape from the noise of the outside world. Well , if i have been too much complex or if it seems that i have blabbered something please do forgive me and please send your feeds to d_sriram@msn.com with the 'subject' of the e-mail as 'yoga'.