I'm trying to create an effect similar to the one used in the title slide of this video: http://www.youtube.com/watch?v=XVPw7kFagE8
Basically, I want to have one textbox fade in at the beginning of the clip, and then another textbox on the same clip fade in a few seconds later. Is that possible?

Yes it is. Put first title clip on track 0, second title clip on track 1. Offset second title clip to the right, but leave it overlapping the clip on track 0. On the composite transition for each title clip, you can leave "with track" set to Auto, or you can set it to Black. Then add fade from black and fade to black video effects to each title clip.

Thanks for the reply!
I tried what you said, but I'm probably doing something wrong because all I'm getting is the bottom text replacing the top text instead of overlayed on top.

I've attached what I'm trying right now. Could you please correct what I'm doing?

Also, is there a difference between using the dissolve transition and the fade in/out effect? Currently in my video, I'm using dissolve and I'm not sure whether I should switch to fade in/out.

Hm, after playing around with it some more I think I got it.
I set the background of the bottom title clip to 0% opacity and then placed it on track 0 with auto composite. The top title clip was placed on track 1.

I looked at your project, and I see you gave your title clips a non-transparent background. In my explanation I assumed you would be leaving the background of the top clip transparent, so the text from the bottom clip would show through.

There is nothing wrong with using dissolve transitions at the ends instead of the fade from/to black video effect if that's what you prefer.