I just did this today, following the instructions available at:
http://personal.bgsu.edu/~bombich/mactips/swap.html
Personally I don't se much of a speed-boost. Perhaps it's because I don't use any applications yet that would profit from this configuration.
//megus
B&W G3 400 MHz
448 Mb RAM
6+4 Gb HD
iBook SE 466 MHz
192 Mb RAM
10 Gb HD