Set form scaled to false. Most vista machines will be in normal 96dpi.

Use DelphiX for your app - it is easy to learn and will work on a wide range of machines and hardware types. I made a maths cdrom a number of years ago using delphix and it works on just about anything. We get no complaints about compatibility problems.

Obviously DelphiX has a few limitations but nothing that would hinder you for this project.