I believe wireless printing requires an AirPort Extreme base station. I don't think the older ones had a USB port (though, my first base station was an AP Extreme so I can't vouch.) However, the Extreme base stations work flawlessly with the old AP cards (this I can vouch for).
As far as download speeds, as long as you have a good signal, there is no performance hit to a cable modem. Airport handles my max 400k/s throughput just as well as CAT-5. Interference or something could slow it down, but unless your base station is on your running microwave while you are gabbing away on you 2.4mhz phone, and downloading the latest LOTR trailer, you shouldn't notice anything.
Printing, I've noticed, varies. My old printer, an Epson 820 Photo Stylus, would really slow down when printing large, high-res pictures over airport (vs. over USB). My new printer, a Cannon i950, prints just as fast either way. So, I guess you might want to ask if anyone has tried it with your printer.
Hope I've cleared things up a bit.
Cheers!