Ok, I've gotten it working. Thanks for the help.
As it turns out, my problems were being caused by having not changed /etc/cups/mime.types and /etc/cups/mime.convs to enable raw printing. I'd also done something dumb, by not having installed ghostscript or a2ps on either of my Linux systems (laptop or desktop).
See, until quite recently, the printer in question was decidedly in the "WinPrinter" category. Until recently, I had never found a usable driver, and the last time I installed my linux systems, I decided to save a little hard drive space. After finding a driver on www.linuxprinting.org
that actually worked, I decided to give networking the piece of junk another go.
So... install ghostscript and a2ps on the laptop/desktop, and half of my problems are gone. I'm able to print through CUPS using exactly the URI that I'd figured out previously.
Now I have to get Windows interoperability working. She-who-shall-be-obeyed prefers Windows, because she insists on using MS Office. I've had all the arguments, and there's no sense trying to convert her.
Because I didn't have mime types enabled, and because Windows error messages were utterly useless, I'd assumed that Windows was having the same problem as Linux. It wasn't. Once I enabled raw printing in the mime files (at the bottom), I was able to get Windows working with IPP, as well.
Funnily enough, I hadn't even realized that raw printing was off by default until I said screw it, and started trying to get it working through Samba. Once I read the Samba.org documentation, specifically the "common errors", I realized my mistake, and fixed it in about 5 seconds. They should really put that somewhere obvious in the CUPS documentation.
And if anybody is wondering why the essay, it's just in case somebody else has the same problem. I'll go nurse my shattered ego, now....