Since the payroll tax tables have changed/lowered on my paycheck, how will this affect my 2018 taxes when I file federal/state taxes next year?

The withholding tables have been adjusted to reflect the new tax rate and bracket changes for 2018. You can see in the chart below the new changes. You may want to adjust your W-4 withholding if you determine that the new rates/brackets will affect your personal tax liability/refund.

Note: Personal exemptions have been eliminated and standard deductions have increased.

http://www.businessinsider.com/tax-brackets-2018-trump-tax-plan-chart-2017-12