I's just yankin your chain... But, ya this would be simple.
The problem with serial > USB converters would be drivers. Sure you could get them, probably. But why set yourself up for driver-dependence? The PLW NT is old, but not that old. Should be no problem at all. Worst case, he'd have to use Gimp-Print, which is no big deal. I just check in Print Center and the driver for the PLW NTR is there and that would probably work for the NT as well. If you still have doubts, though, call Asante tech support or sales. They're real helpful. It's not a very big company, so you can usually get through quick (relatively).
To set the printer up, just plug everything in and power it all up. This will be the trickiest part. The AsanteTalk and printer need to be turned on in a certain order. Can never remember which way though... Then open Print Center and click Add in printer list. Select AppleTalk. The printer will show up beneath. Select a PPD. Click Add. Done. Just as easy as USB. And if he's got (or will get) a LAN set up, he can plug it into the switch/router and set it up EXACTLY the same way from any computer on the LAN.
I just thought of something... I used to have one of those printers. It seems to me that you can buy an upgrade for the NT to the NTR. Just in case the NT is not supported (which I doubt).