Platform shooting game

Hey
Im planning out a platform game in my head just for fun nothing serious.
Anyway I know how to make dudes move and stuff and i have a few tricks up my sleve for enemy ai ;). Anyway i just want to know 3 things.

1 - If my dude falls with a simple hittest script he will end up a bit in the floor, how can i get round this so he lands perfectly on the floor?
2 - If i have an angle and an x and y point for a bullet that doesnt really exist how can i check what the first thing my non-existant bullet hits in a straight line?
3 - How can I make my charator walk up slops, kind related to question one.

Thanks for your help
Dan

This is the best game in flash http://www.strille.net/works/misc/platform_demo/