Hi Eustace,
An RIP server is a printer/color profile manager that maximizes color fidelity output.
Couldn't your friend get a serial-USB adaptor and connect the 1520 to his G4?
Why is he printing from OS9? Is that because the RIP software is OS9. If he can get his 1520 happily operating from his G4 (or OSX in general), can he use that RIP or does he need to upgrade that to an OSX version?
I do know that when I first upgraded to OSX, I was frustrated with some printing because I got better results on my Epson 1270 in OS9. That's when I experimented with Gimp Print, but found it a bit difficult to get the color fidelity settings correct with Gimp Print (at least for picky me).
If your friend is using Photoshop in OSX, he may want to try managing his color output from within Photoshop, rather than relying on the RIP or Epson. When he has a file ready to print, he can press command-P, and he'll get Photoshop's print setup screen. He should check "advanced" or "more options" (can't remember how it's worded) at bottom of screen. Input source is "document". Output source would be the 1520 paper that he's using (something like "Epson 1520 photo paper") -- there should be a drop-down list of choices. Most output is fine with "relative colormetric" and "black point compensation" both checked. Then, when he pushes the "print" button, he'll be taken to the Epson printing window. There, he should make sure the paper selection matches the paper he selected in Photoshop and then select "NO COLOR MANAGEMENT". This will put Photoshop in charge color. I've had excellent results with two different Epson printers using this work flow.
Epson may not have 1520 drivers for OSX. If that is the case, he might want to try working with Gimp Print in OSX. He'll have to experiment a bit with the different color settings, but once he has it to his liking, he can save those settings and print happily. I just haven't taken the time to do that experimenting yet. It's an excellent program and FREE. There's also a forum for GimpPrint here --
http://sourceforge.net/forum/?group_id=1537
Apologies if all that is either redundant or does not apply to your friend's situation. I've never worked with a RIP, so don't know how it affects workflow, but I've had gallery-quality output without one.
Hope this has been a little helpful ...
Tina