Hi -- I'm a 4th year med student who had a terrible time the summer before med school waiting on a waitlist that never panned out. I must caution you against making the same mistake as me. What I did was to translate (in my head) a waitlist into a probable (late) acceptance because I wanted the school so badly.
The way I read their letter is that they have 2 waitlists -- one is their top priority list and it is ranked from those they want the most to the least, and those people will get accepted in that order as spots open up. The second list (the one you are in) is a bunch of alternates -- these are people that they liked enough that they didn't want to reject them, but didn't like enough to accept them or put them on the ranked list. If they run out of people on their ranked list (which from their letter sounds like it doesn't usually happen until July), then they'll go through the whole other "alternate list" and pick new ones to add to the ranked list.
To assess your chances of getting in eventually, you'd need to know how many people are on the ranked list and how many other people are in the alternate pool. But for your own sanity, I would take this as having a SLIM chance of working out -- in other words assume your going to the other school and that it won't work out at UCLA.
In the meantime, keep letting them know you're interested -- e.g., write them a thank you letter for their interest in you and in it, reiterate all the reasons you are super interested in UCLA. In June, you may write again to let them know how interested you still are and update them on your last set of grades (if they're good).
Then July 1, give them a call and ask them your chances, explaining about the other school starting soon. The point of all of these communications is NOT to be a pest (be super polite and DON'T go overboard) but to make sure you keep letting them know you're interested and enthusiastic about UCLA so that if they have to dip into the alternate pool, maybe they'll think of you more quickly.
Wait lists SUCK -- there's no way around it. But try to concentrate on the positive -- at least you have an acceptance and you know that next year at this time, you'll be working your MD.
Hope this helped,
zb
[This message has been edited by zb (edited 03-10-2001).]