If you have one of these clever domain name forwarding to point a blah.com to myisp.homespace.com/blah. Dont ever, ever change the URI setting for your wordpress blog to match the new blah.com.
You’ll quickly find your stylesheets not found because blah.com/stylesheet doesn’t equate to myisp.homespace.com/blah/stylesheet. Not only that, the wp-admin wont let you in because everything is pointing to the wrong spot.
WordPress Site URL Guide will tell you to do something like
update wp_options set option_value=’http://correct/uri’ where option_name=’siteurl’;
and shows how you’d do it in PHP myAdmin