Kudos to hink, for pointing me at Limp. It looks like it should do exactly what I need (though MoviX also looked like that before it failed to run, but I am enheartened to learn that there's another option).

However, by the time I'd read his comment (ie. Ten minutes ago), I'd already solved the problem. So, where was I?

Day Two:
21. Boot off the slack bootdisk. Boot failed. Investigate
22. Try about fifteen other things before I realize that the boot failed because the disk was bad. Write another.
23. And another...
24. And another.... I should point out that I haven't bought a floppy disk in about ten years, so I'm just using the massive pile of old discs I've had sitting around since '95.
25. It boots! Write a root disk
26. And another...
27. And another...
28. Hey, that's a bash prompt! Let's try installing...
29. "Lost interrupt"? WTF?
30. Okay. Worked that time. Install me just enough slack to get going.
31. Hey, the BIOS never made that alarm sound before.
32. But it seems not to care.
33. Okay. I'm linuxing!
34. Let's try inserting a USB pen drive.
35. Kernel Panic. Retry.
36. etc.
37. Okay. Giving up on USB. Remove the PCI usb card because I'll use that for something else I guess
38. Mount the CDROM and try to play an MP3
39. What do you mean no sound?
40. Run ALSA configuratior. It flashes "Found 2 sound cards" then tells me it didn't find any.
41. I bet it's...
42. Yep. Reinstall the ALSA packages. Now it finds the sound card.
43. But none of the mp3 players I installed work. Something about a library...
44. Which also wasn't installed. Install it.
45. And another.
46. And another.
47. And, lo, an episode of Yours Truly, Johnny Dollar starts playing.
48. Okay. Now I need some controls...
49. Knit 1. Perl 2.
50. Cobble together a perl program that builds a playlist and then plays it. Have the program check which signal amp died from to detect whether to go to the next file on the list or the previous one.
51. Cobble together a perl program to respond to keyboard input by sending a SIGSTOP, SIGCONT, SIGTERM, or SIGHUP to amp.
52. Huh. Amp always dies from a SIGPIPE. WTF?
53. Oh. I'm killing the wrong process.
54. Success!
55. Edit inittab to launch the player and control program automagically.
56. Catastrophic failure! You can't just launch arbitrary programs from inittab if they want to talk to the real world.
57. Coax getty into running the program for me.
58. Success! Sleep mode

Day Three:
59. The thought occurs t ome that it would be mechanically simpler to accept input via the mouse.
60. Gut a mouse
61. Think long and hard about how to do this.
62. Start GPM
63. Write a perl function that opens a pipe to mev and parses its output, turning leftward, rightward, upward, or downward movement into a a single character
64. Test it. Hey! It works!
65. Replace the keyboard input bit of my controller with the mouse input bit
66. It doesn't work
67. Huh. Calling a function doesn't store the result in $_. Learn something new every day
68. Yay it works!
69. Oh. It crashed.
70. Stick a half second sleep in the controller program to keep it from responding to a zillion mouse events for every gesture
71. Success. Turn the damned thing off and do some real work.