For those of who who are glued to Yahoo Messenger! chat here’s a collection of 16 Messenger themes:

Themes

a LiL Bit Girly byNiKY
black widow
Blue Jeans
BlueSky
Bronze
Celadon
Gel LED(green)
Grayorange
half_life2
Indigo
Maverick
Metallic Black
Pink
ToeBee’s_Skins
XBOX 360
Hot Rod
Silver
Woody
Y! Vista

Installation

Download and unzip the theme to:-

Install Path
Unless you’re installing a Yahoo! Messenger version 5.6 skin, which are located at
C:\Program Files\Yahoo!\Messenger\skins\{skin name}
you will need to install / unpack all your skins (v6-v8.1) to
C:\Program Files\Yahoo!\Shared\Graphics\{skin name}

So for your v6, v7, v7.5, v8 and v8.1 skins to be available for access from within Yahoo! Messenger they MUST be installed to:
C:\Program Files\Yahoo!\Shared\Graphics\
and they MUST be in the correct, and their own, folder
C:\Program Files\Yahoo!\Shared\Graphics\{skin name}