Lease/purchase - the MOE line is usually lease & someone you should talk to is Jonathan Beveridge - exMOE but currently working for Equico. He is their educational consultant. He is really good at talking this through and can work with you (for free) to develop your long term planning for infrastructure management. Jonathan will be in Taranaki next week I encourage you to invite him to your school to critique & give advice on your ICT Management Plan - if you haven't got one - well you really need Jonathan to come to your school!!!
Having said that it also depends on your funding. Many of our schools find themselves with a sum of money to spend on IT that has come from a grant & they spend it on hardware. One of my schools bought a pod of laptops - I investigated this for them & looked @ the lease/purchase question but because they had the sum of money now & didn't know what funding they would have at the end of a lease term (usually 3 years) they decided to purchase instead.
Leasing means that you should have a steady budget for your ICT needs but it is the most sensible option to have a long term plan of hardware maintenance & upgrade.
Even though Jonathan works for a leasing company you don't necessarily have to go with Equico to provide your equipment - same as if you were purchasing - investigate all the options.