How to do ranges in vb2008

Question

we're tasked to make a EMPLOYEE PAYROLL SYSTEM as our project for our OJT..
we're lucky we've done most of the needed functions of the program but then, the main function is not yet done -- THE COMPUTATION of EMPLOYEE SALARY..

now, using textboxes, we're trying to do inputing amounts on textboxes then the equivalent value will be displayed automatically in the next textbox or in the textbox that need that value..

The Payroll System is composed of:

Basic Salary (value to be manually entered)
Semi-salary = basic salary / 2 (automatically displayed)
Overtime (value to be manually entered)
Income Tax (automatically displays the equivalent value to be deducted in the salary according to its range)
SSS Premium (automatically displays the equivalent value to be deducted in the salary according to its range)
Pag-ibig Premium (automatically displays the equivalent value to be deducted in the salary according to its range)
Philhealth Premium (automatically displays the equivalent value to be deducted in the salary according to its range)
Tardiness (value to be manually entered)
Sickly (value to be manually entered with condition of how long it will be payed, days/months)
SSS Loan (value to be manually entered with condition of how long it will be payed, days/months)
Pag-ibig Loan (value to be manually entered); and
Cash Advance (value to be manually entered)


...please do guide us help us in doing the Tax, SSS, Pag-ibig and Philhealth Process..
(They have ranges and equivalent amount to be deducted in the salary)



we don't know how to code their condition, we're just beginners in using VB2008 so we don't know the crirical parts...
please help us.... :C :C