Dynamic page creator like TagWorld?

I was checking out www.tagworld.com. I think it would be tough, but does anybody even know how to BEGIN making a dynamic profile generator like they use? That would be invaluable for admins, I'm sure.

Basically, TagWorld lets users create a profile using on-the-fly blocks to litter a page. It's very fast-moving and results in really customizable pages. It's probably one of the best page-making set-ups I've seen for any site, period.

EDIT: Live Spaces (http://spaces.live.com) uses the same sort of system.