Code can be displayed in filtered HTML or  full HTML. To display code, you have two solutions:

1. Use the regular <pre></pre> HTML tags
2. Use the <code></code> tag

Using the second, Drupal will format your code using the VIM-color module. Note that the <code> syntax can recognize code automatically from the first line like in

<code>
#!/usr/local/bin/perl
use DBI;
print "Hello world\n";
</code>    

which will be displayed as

unlike the use of <pre></pre> which would display

#!/usr/local/bin/perl
use DBI;
print "Hello world\n";

but, if you use the Full HTML mode, you could also "force" perl formating by using

<code type="perl">
use DBI;
print "Hello world\n"; 
</code>

which will display exactly the same as above.

WARNING: Note that switching between enable rich-text and normal mode while using <code> may scramble your formating. This was also noted in How to create a cross-reference to another page.