slackware works fine in qemu on windows. install kqemu as well to make things run quicker.
If you want your virtual slack pc to appear on your real network, install openvpn, and bridge the tap adapter and your real adapter. (works with a host of xp or higher)
If you want to run more than one virtual machine at the same time set processor affinity to both processors (for a dual-core system) for each qemu process. This shares the load out more.
I created a 10gb virtual disk. this is plenty for a full install of slack 12.1 or current with some spare for playing with.
When installing, use the classic (text-only) options for the system terminal and lilo. xwindows will run fine once everything is installed, but you need to add some kernel options to get rid of clock errors. These can be added in lilo.conf
I can post more info if you are interested.