The keyboard speed has two components: delay (before a key that you hold
 down starts repeating) and typematic rate (the speed once the key starts
 repeating). Most BIOS versions since 1986 let software change the delay
 and typematic rate by calling INT 16 AH=3, "set typematic rate and
 delay"; see Ralf Brown's interrupt list <Q:02.03> [What and where is
 Ralf Brown's interrupt list?]. If you have DOS 4.0 or later, you can use
 the MODE CON command that you'll find in your DOS manual.

 On 83-key keyboards (mostly XTs), the delay and typematic rate can't
 easily be changed. According to PC Magazine 15 Jan 1991 (x: 1) page 409,
 to adjust the typematic rate you need "a memory-resident program which
 simply '[watches]' the keyboard to see if you're holding down a key .
 and after a certain time [starts] stuffing extra copies of the held-down
 key into the buffer." No source code is given in that issue; but the
 QUICKEYS utility that PC Magazine published in 1986 does this sort of
 watching (not verified); source and object code are downloadable from
 <http://www.simtel.net/pub/pd/48667.html>