in reply to Parsing a page that requires login?
If you are asking to check a person's my.yahoo.com site *without* knowing their username and password, well, see merlyn's post above and shame on you, you 7331 h4x0r! :)
However, if I am understanding your question correctly, and you do have the username and password, you are able to create such "headless" clients using the LWP module. I know that there are some examples in the documentation