well, I can't offer you any sbs tute, mainly coz I just spent the last week on
building my own first model ( ==quite an O2 n00b myself ). ;D
but my model works great (its a tank, yup, a rough start indeed) and has great textures as well, so I know enough to tell ya THIS dood :
modelling/texturing is basically sitting 200 hours in front of a screen,
making something that it only takes 1 second to delete!
(yeah, I did that too - dooh!!! )
;D
anyway m8, once you have O2 installed it won't take ya much more then a day or three to read, test & understand the avaliable tutorials.
But an AT-AT is to my knowledge a starwars vehicle and thus not really for realism-combat ofp sites like ofpec (
not sure but I think thats the politics around... used to be.)
And yer vehicle would only be a gliding static object (perhaps with a "turret" head)
as the 4-legs walker animation isn't created (yet) for the ofp engine.
it could be fun though to see a total star wars mod for ofp, but thats prolly a job outside ofpec, maybe by starting your own mod site ?!
you can always upload the models to some site (ofp.cz or alike) and hope that someone wanna do it for ya?!)