You can hit Q and/or control^C anytime after about 10 seconds after applying power to the player.

And there's a space after "cat":

cat  /proc/meminfo

Alternatively, if Hijack is installed, you may be able to connect to it's webserver over ethernet and view it there: http://players.ip.addr/proc/meminfo

Finally, this is not even needed.. instead, you could just watch the serial output during boot, looking for this line:

Memory: 31240k/32M available (980k code, 20k reserved, 524k data, 4k init)

Cheers