1) spike and xander get together just before sunnydale goes down. xander gets a tattoo on his wrist for the number of days they had. he ends up working for a film company as the set carpenter and he's got an on again/off again thing with one of the actors.
2) teenage xander gets bought or adopted by giles. giles's son spike seduces him; giles seduces him. there's alot of seduction. i remember one scene in the back of a limo and one in giles's office. sorry i don't have more detail.