Perl, 76 chars

Run with perl -M5.010.

$-=rand 6;$_="-----\n|0 2|\n|4";s/\d/$->$&?o:$"/ge;say$_,$-&1?$":o,~~reverse

If you find yourself wondering what the heck the $->$ operation does, the following reading notes may be helpful:

• The variable $- automatically truncates its assigned value to an integer.

• The variable $" is preset to a single space.

• o is a bareword (representing "o").

Perl, 74 chars

Run with perl -M5.010.

$-=rand 6;$_="-----
|0 2|
|4";s/\d/$->$&?o:$"/ge;say$_,$-&1?$":o,~~reverse

(Note that the newlines in the listing are part of the string, and not just inserted for legibility.)

If you find yourself wondering what the heck the $->$ operation does, the following reading notes may be helpful:

• The variable $- automatically truncates its assigned value to an integer.

• The variable $" is preset to a single space.

• o is a bareword (representing "o").