I use Xandros Linux as my main system, I have Windows 98SE on another partition that I don't really use. So you could dual boot it with another Windows system if you want.
If you don't want to load Linux on straight away I would recommend using what they call a live CD, it's a bootable CD that loads the operating system into memory, it supposed to be slower than running from the hard disk, but that depends on how much memory you have. I have tried Knoppix click here and it is extremely good, there lots of interesting tools on there that don't come with Windows. Running a live CD also allows you to check that your system is capable of running Linux.