Yahoo is set to release a software update for its web based e-mail users later today. Among the new features is a program that allows users to send text messages from their PC directly to cell phone users. The enhancements make it easier to send e-mail, instant messages or text messages from a single Web site - no need to launch or toggle between separate applications or devices. It will take up to six weeks for all the new features to become available to all 254 million Yahoo Mail subscribers in 21 languages worldwide.