I forgot to say you can put the ipks onto SD.
When you install them it will ask whether you want to install to ram, sd, or cf. I recommend you buy an SD (128MB does me fine) and install as many of your apps onto SD (you will need to keep it in the zaurus at all times). The onboard ram fills up quickly. if you install into ram it will run quicker, but alot of people find SD installed programs to be quick enough.