i think it would be a fairly simple DIY project. (probably a bit of hard physical labour though, lugging sleepers around and levelling out a spot in the garden etc )
a good quality liner possibly with some underlay should do the trick. as long as theres no sharp splintery bits on the wood to pierce the liner!
have a look on the web, theres quite a few DIY guides.
don't think i've seen that sort of pond on this forum though, perhaps you can be the guinea pig
I would personally go with railway sleepers they look a bit nicer than the pine ones, but thats just me
good luck with it.