My first impression is there's two things you could consider doing.
1) You could move the steps (which you currently have in the left hand column) to a top bar of the wizard, and have the steps always be present. The area underneath the top bar (let's call it the "content box") would always be visible.
That means, if the user is completing Step 1 and selects a checkbox, the fields would display in the "content box"-- but not in a separate scrollable box. If the user scrolls down, the info in the "context box" would scroll, but the top bar (containing the steps) would always remain present.
2) If you'd rather keep the steps in the left-hand column, you could have the right hand column behave in a similar way that I described above. For example, if the user clicks a checkbox, the fields appear below it (but not in a separate scrollable box you have wireframes). Instead, they would just appear below the checkbox, and the user can scroll within all of the "content box" info in the right-hand column of your wizard. The left-hand content (containing the "steps") would not move as the user scrolls.
Let me know if any of this is unclear and I can try to clarify!