Hi -- the cable is the same for the 5000 and 5700 (and entire Classic Zaurus series).To find the specific differences between the models, goto:
http://personal.nbnet.nb.ca/landryj/zaurus/main/new_zaurus_pages.htm
Click on 'Z Models' (off to the right, I believe).
If I remember right, the real differences are that the 5700 has better power management, especially in the use of PC Cards, and includes a Spreadsheet with some very useful templates as well (even if you don't use spreadsheets, you'll find learning to use the Z's adds some real helpful capability!).
If you're thinking about getting a more capable model, may I suggest the 5800, which is the same as the 5700 but with 2 Meg of memory and a backlight. The 3500x has all the same functionality as the 5800, but is smaller (more coat-pocketable but smaller screen and a bit smaller keys) and includes an internal 14.4 fax/modem and slightly updated IR link interface (still pretty old, though)... but it lacks a PC Card slot.
Regards,
Skyler