Do you mean for avatar use?
WinXP has a powertoys tool you can download and install off of Microsoft's website that can resize images through windows explorer. Search for power tools. Look for something called image resizer (there's only half a dozen of these power tools, or so).
barring that, any general image editing software can do it. MS Paint might even be able to.
P.S. I'd do it myself for ya (only takes a minute) but I'm not at my own PC.