Yahoo messenger for windows vista will have some cool new features, tabbed IMing being the prominent among those.
With tabbed windows you can easily switch over to different chat windows.
A hidden hack inside the current version of yahoo messenger enables you to enjoy the features of windows vista version of messenger in your current version that is yahoo messenger 8.1.
You can download this Tabbed Im hack for your version 8.1 here .. http://www.wackyb.net/utils/WackyB-YIM-IMTab-Fix.msi