When I did this on my 5300CS I just used linux's standard is writer to the card through a USB reader. It worked right off the bat for me, although for any custom file transfers I used sheepshaver to emulate a ppc and use a similar method to what Rajel said although I just unstuff .Sit and move those files on to keep the resource fork intact.
But, I think Rajel's method is better than writing the iso. Using an emulator and an iso on a modern PC will mean installation is much, much faster, so that's probably superior for ease of use. However, just wanted to say that simply writing the iso to the card works fine. After you install, you just need to write over the card again to get full capacity back.