I use Mozilla Firefox browser on my Windows7 machine for this very reason....
Install Mozilla Firefox ..... go to tools then applications then mail to drop down box, select Use Yahoo Mail....for some reason Windows 7 will not let you choose yahoo mail in the IE browser. I use IE 8 in a Vista and XP machine and the option for yahoo mail as default is available... I have read that the yahoo plus mail is an option ........

could it be that yahoo is working on being a paid service....
another choice would be to set up the pop mail to go to outlook express...i have not used outlook express for years..
Have a Great Day
~~Dawn