I tried to copy blk* but the client on the new machine wasn't able to open the files.
error message:
Loading block index...
EXCEPTION: 11DbException
Db::open: Das Argument ist ungültig
bitcoin in Runaway exception
EnvShutdown exception: DbEnv::close: Das Argument ist ungültig (22)
("Das Argument ist ungültig" = "the argument is invalid")
Since the client on the old machine is working proper, the blockchain files shouldn't be corrupt.