Steady on, before you rush off and buy something. Boot camp is free and allows you to install Windows on a Mac, it just means you can't be using both at the same time. On bootup you have a choice of whether to use Leopard or Windows, or whatever OS you choose to install.
Virtualization software allows you to run another OS at the same time. So you boot up into Leopard, and then can use Windows from inside there. I'm not sure about performance, but I'd expect it to be lower than using Bootcamp, plus you have the problem of having to pay for it.