It does work in OS 9 as well, and it is easier to set up. Open the Memory control panel. In the Virtual Memory section, there is a pop-up menu to choose the partition for the swap file.
Of course, you get the most speedup from real RAM. And real RAM is so cheap right now that there is no excuse on a modern machine not to upgrade. I have 320 MB, and OS X does not normally page anything out to disk at all. I have VM turned off in OS 9, and have never regretted it.
You can get a 256 MB PC133 for US$41 or a 512 MB PC133 for US$120. Note that PC133 will work in a PC100 or PC66 PowerMac (everything from the beige G3 onwards). SODIMMs for iMacs & laptops cost a little more, but still dirt cheap compared to the past.