Try SuSE perhaps
I've installed OpenSuSE 10.0 on a few Windoze boxes with no difficulties. The installation automatically created a new partition, reducing the Windoze partition (on XP and 98) enough to install Linux, but not crippling Windoze in the process. It then set up Linux with the Grub boot loader and had Windoze in the menu, so you could boot up into Windoze at will, with no ill effects. The default was set to Linux, but it can easily be set to default to Windoze if you prefer.
I'm sure other distributions are also capable of doing this just as painlessly, but I only have experience with SuSE. I've found it to work very smoothly, including on my laptop with wireless. I rarely ever boot Windoze any more.