i'm thinking its memory.. but you said it crashed every time you jumped on a flying mount.

try this: come in fresh.. don't move.. and jump on the mount. does it crash?
if so... then run your wows... then on keyclone, right-click remove both.. so they are running but not connected.. then try mounting. same problem? then its a blizzard or hardware issue.

let me know how it goes.

g'luck,

Rob