I have every achievement (and avatar award) except for the addicted achievement, so yes, they are all physically possible.
That's awesome, Poppy. Would you consider putting together a guide for: http://www.xbox360achievements.org/game/spelunky/achievements/
...Or at least making posts in the discussion sections on the hardest achievements?
For use people who have never played Spelunky prior to the Xbox release, these achievements seem daunting, to say the least. And there's no achievement guide.
If you were to give us pointers on how you did it, that would help a ton.