IRS Online Withholding Calculator
You can fill out and print these forms with the free Acrobat Reader or better.
If you need to save forms, you'll need the full Acrobat or Acrobat Approval.
The IRS is offering free copies of Acrobat Approval 5.0 in its free "Small Business Resource Guide CD-ROM"
Normal IRS PDFs (non-fillable)
PDF forms you can fill in on your computer