I use the "Enhanced Steam" by TDD. http://forums.steampowered.com/forums/showthread.php?t=1197385
From: Sain_of_Caelin | #003 Looks a bit confusing for something that doesn't make Steam look way better. Meh.
Confusing? 1) Download skin you want 2) Unzip/rar/ect the folder. 3) Drop folder into your [...]\Steam\skins folder. 4) Open Steam, click "Settings", click the "Interface" tab, click the drop-down for skin selection. Choose the skin you just installed. 5) Restart Steam and you're DONE.
Plus there's a TON of skins out there that can style it to anyone's preference.