I don't think they do it any differently than other schools. When you fill out the AADSAS application, you enter your grades from college (you have the option of putting +/-'s or things like AB etc). My transcript was pretty straight forward, so I didn't have any problems entering my grades, but you can always talk to your registrar or call AADSAS for some help.
Like Dentgirl09 said, they rank their applicants. They look at more than GPA and DAT though, they have many factors that they consider (volunteering, observation, extracurriculars) and each one has a different percent value. For example if you have tons of volunteering and say volunteer experience makes up 20% of the number grade they give you, then you get 20 pts. After they assign "grades" to each part of your app, they compare your total grade to other applicants' and interview those with the highest ones. Sorry if this is a little confusing, I'm relaying info I got at the interview a couple of months ago so it may be a little off, but you can always call the admissions office, they're pretty helpful. Good luck!
