Custom Validation Script

I need to be able to have a form with various fields to do computations based on various ranges. However, the best I have been able to come up with is the field range option which give me 0, 1 and 2 as options for the user on the form. The problem I have is that I need to exclude the 1. The solution I have been seeing but not able to do myself is the custom validation script. Is begging appropriate?   I would really appreciate it.