Mark is a guy living in the U.K. who makes stuff, like this awesome steam-powered AT-AT. This talented sculptor prefers to go by the name Captain Bayley, so it only makes sense that his steampunk creation would be called "Captain Bayley's Infernal Mechano-Perambulator."
Not only that, but Captain Bayley gave his Infernal Mechano-Perambulator as an engagement to his fiancé, Caroline. Aww. Here's Captain Bayley discussing this project:
'Captain Bayley' initially made this fair creature for another, his bride to be, as an engagement gift (initially our AT-ATs were acquired as christmas gifts, yet soon developed a life of their own (radios, 1930 camouflage and finally weathered maritime [some prefere to call her 'Steampunk']) however this one stood taller than the rest.
There you have it. Contact Mark on his website to request information on custom work or visit his flickr to see tons more pics, but don't bother asking to buy the steampunk AT-AT, because it isn't for sale.