EDIT: On watching the video, I realised that the video cuts out before I get the "No Hard Hat Required" achievement. Basically, do a full lap of the full-pipe and you'll get it.
Shows you how to get:
Skylight Superstar - 25G
Drop into Rob's plaza through the skylight
No Hard Hat Required - 25G
Touch the top of the construction full-pipe
Yes, yes, I know, I bailed both times. I bought points today, bought the DLC and played Skate 2 for the first time in about a week now, thanks to Street Fighter 4. So, sue me.
Anyways, hope you get the achievements. :)