I'd second what the others are saying , new green oak sleepers not a great idea
that said i have resawn numerous old sleepers and IMO chainsaw is the only realistic way to go (providing as someone else said that you know what you are doing and have the appropriate safety gear )
my approach is to first give them a good clean up with a pressure washer and yard brush - this removes most of the grit and sh*t and enables you to see if there are any big lumps of metal included.
Assuming there arent I then lay them accross two battens and rip and cross cut them down the middle on both length and width
this produces 4 bits that are ball park 6" x 4" x 4ft which can then be further resawn with the bandsaw.
If there are metal inclusions I draw a line either side and cut that bit out with the chainsaw first.
Be aware that you will need to regularly resharpen your chain , and that you will need a decent powerful saw - a cheap DIY shed electic C/saw is not man enough for the job.
All things considered if you are new to working wood and not a chainsaw expert , forgetting the sleepers and going to a decent timber yard is the way forward - for example UK Oak
http://www.uk-oak.co.uk/product-catalog ... _and_Posts! will do decent prices on most common dimensions.