There is a brand-new Windows 7 Theme available for Vista.
The theme uses some parts of the Windows 7 beta, hence it looks very promising.

You can install it on Vista SP1 x86 and supposedly on x64 systems.

The changelog is pretty impressive:

•  Taskbar buttons with shadow
•  Size, Type, Name images
•  Flashing button
•  Favourite list text colour (black)
•  Shellstyle
•  Start menu margins
•  Shell32.dll colour animation
•  Added normal PDC taskbar
•  Fixed the STREAM
•  Variant
•  Black text when windows are maximized
•  Added Text Glow Ehen Windows are Maximized
•  Start menu
•  Taskbar images
•  Hover images
•  Copy-Paste animation
•  Quick lunch hover images
•  Updated taskbar buttons
•  Added Normal Taskbar
•  Added some x64 system files (but not the style)
•  Fixed favorite links pane to look like Windows 7
•  Added text glow on maximized windows
•  Update the taskbar
•  Update the taskbar buttons
•  Redesigned the Aero Peek
•  Added the PDC Orb
•  Fixed start menu margins
•  Added New Taskbar Buttons
•  Strong and Clear Aero Borders (like in win7)
•  Fixed Active and Inactive Borders (like in win7)
•  Changed the Taskbar Buttons Colours (more smooth and glassy
•  Redesigned the “Aero Peek” Button
•  Changed the Min/Max/Close Buttons (Active and Inactive Mode)
•  Added the Real Windows 7 Orb
•  Real Windows 7 askbar Buttons
•  Real Windows 7 Taskbar Size
•  Fixed Tray Icons (Now they are centred)
•  Fixed Basic Style
•  Fixed Normal Taskbar Size
•  Taskbar Style
•  Group Taskbar Buttons
•  STREAM image (again)

Download Windows 7 PDC Style

• 
  Black Ops 2
• 
  Halo 4
• 
  God of War 4
• 
  Crysis 3