Seems everyone loves to laught at the celeron line of processors. At first they had a major design flaw that was corrected within 6 to 12 month.
My Celeron runs Windows 2003 Enterprise edtion, I've also dual booted it with several different variations of linux, XP Home/Pro and Win2k. Runs them all with similar speed as I precieve it. Now I also running whole disk encrytion full time with win 2003 and boots faster that a account with Win 2003 and a Xeon processor.
I did make the correct decision and jacked up the RAM to the system boards max which on my model is 512. If you have no plans on doing 3D gaming, it works great and under normal usage as fast as a pentium to the person using it. If you are concerned with speed your money is best spent on increasing the RAM. Biggest bang for the buck.