sorting by day of the week

p8:owl=>SELECT to_char( logtime, 'Dy'),count(*) FROM logtab WHERE 
date_trunc('day', logtime) > current_date + '7 day ago'::interval group 
by to_char( logtime, 'Dy') ORDER BY to_char( logtime, 'Dy') DESC; to_char | count
---------+------- Wed     |  1447 Tue     |   618 Thu     |  1161 Sun     |   230 Sat     |   362 Mon     |   760 Fri
 |  1281
 
(7 rows)

The problem is that I want those results sorted in day of week order, 
not text order of the day name, so I tried this:

p8:owl=>SELECT to_char( logtime, 'Dy'),count(*) FROM sclog WHERE 
date_trunc('day', logtime) > current_date + '7 day ago'::interval group 
by to_char( logtime, 'Dy') ORDER BY to_char( logtime, 'D') DESC;
ERROR:  column "sclog.logtime" must appear in the GROUP BY clause or be 
used in an aggregate function

Now obviously I don't want to group by logtime (a timestamp) so how do I 
work around this?  What I really need is a function that converts from 
the char representation to a day of week number or vice versa.  I also 
have the same problem with month names.