We at Management 2000, have been helping the employees of our 200 clients (Employers) with possible withholding (W-4) issues for 2009. You see the tables issued to implement the 'Making Work Pay' tax credit may place some employees in a slightly under withheld situation at the end of the year. The web site that I would recommend  you check out is www.irs.gov then go 'special interest' and then click on 'withholding calculator'.
 Make sure you have a current pay stub so you'll have the right data to enter.
If you think this is a pain...well you're right. But that is what Management 2000 does for their clients so that they don't have to. Our client get to do what they do best!!! If this is something you think you would like more information on call me, Steve Schilling at 800-554-5945 or check us out at www.management2000.com