I had this same problem with a site that I did for my brother, and I also purchased from Yahoo...
I forgot we never got this resolved until I read your thread, I look forward to seeing if you get this resolved and how you get it resolved...
Well it's been solved apparently (however the site is still down.. yahoo says it takes 24-48 hours) anyway yahoo was great and emailed me back within 24 hours with this response.
"Hello Tanner,
Thank you for writing to Yahoo! Domains.
I welcome the opportunity to assist you with your concern.
I understand that your website "lastresortpictures.com" does not resolve
without putting 'www' in the URL.
Tanner, as per your test permission, I entered your account and I found
that you have created the CNAME record with the source
"www.lastresortpictures.com", this is why your website works fine with
'www'.
I created another CNAME record with the source
"*.lastresortpictures.com", and now your website is working fine. You
may visit the following URL to view your website:
http://lastresortpictures.com/
Please be aware that it can take 24-48 hours for new records to be
propagated to all nameservers throughout the Internet.
If the problem has not been resolved, clearing your browser's cache and
deleting the cookie files on your computer can often resolve these
issues."
So as usual it was user error on my part... oh well, still in the learning phase of all of this website hosting stuff... hope this helped anyone in a similar boat!