[SloppyGoat]

I could be wrong, but try replacing this

$parseurlchecked="CHECKED";

with this

$parseurlchecked = '';

(That is two single quotes - not one double. Not sure if it matters.)

Or, this is a way that it could be done globally without hacking. Although, I haven't tried it.

'newthread' and 'newreply' templates (I'd guess the edit template too)

Edit the following code in those templates. (Should be pretty self explanitory)

<input type="checkbox" name="parseurl" 
value="yes" $parseurlchecked> <b>Automatically parse URLs:</b>
automatically adds http://and around internet addresses.