Please note that this will not work with some keyboards.
The typematic rate can be adjusted using mode in the following manner:
MODE CON: rate=32 delay=1
The example above sets the rate to 32, but a number between 1 and 32
(inclusive) could be entered instead. This will set the rate at which
characters will be repeated when you hold down a key. 32 is the fastest
and 1 is the slowest.
Delay sets how long you have to hold down the key before it will repeat.
You can set this to any number between 1 and 4 (inclusive). 1 is 0.25 of
a second, 2 is 0.5 of a second and so on.
While this can be typed at the command line its probably best placed in your
AUTOEXEC.BAT file, once you have determined the values you are happy with.