newbie: confusion about attachments

[Stuart McLean <makhector@gmail.com>]

Hi

I have been using gnus for a little while, but rarely send
attachments. As far as I can tell you attach a file via `C-a' and
proceed with the prompts from there.

Let's say I want to send a png as a test to a webmail account like
yahoo. In the Message buffer I type `C-a' and at the prompts type the
file I want to attach, type "image/png", a comment, and a disposition
of "attachment.

I then send the file with `C-c C-c'. I log into my webmail account and
the attachment shows up as text. I have read what I think are the
relevant sections of the Gnus, Message, and Emacs MIME manuals, but I
remain confused as to what variables I might set to have the
attachment displayed properly. Any pointers to info, functions or
variables would be greatly appreciated.

Thanks,

Stuart