I'm roadwarrior-ing this week for the first time with my portable Canon printer. I had installed the drivers for X before leaving home, but discovered later that I needed to print via a "Classic" app, too. So I did exactly as Kelly et al suggested. The CD with the i70 carried both sets of drivers.
FWIW, and because I have 9.2 on a separate partition, booting into it directly seemed to be the safest way to assure that both the X drivers and the 9x drivers "stayed in their proper place".
The instructions for the i70 prescribed that it "would not print" in Classic. That, fortunately, does not mean it will not print in 9x, when the trusty Pismo (with two separate sets of drivers appropriately installed) is booted via 9x . . . at least that's how it's working out.