AeroVG theme is one of the most popular themes available for Windows Vista. It provides excellent transparency in Taskbar, Start Menu, Explorer, etc. and also changes lots of visual things like Menu bar, Address bar, Progress bar, and much more. The theme was developed by Vishal Gupta, a Windows Desktop Experience MVP from India.
After a lot of reader requests for a similar theme for Windows 7, Vishal succumbed to the temptation and came up with the first beta of AeroVG Se7en theme.
You can download it using following link: Download "AeroVG Se7en" Theme for Windows 7. Also, check his tutorial which guides you to install and use custom themes on Windows 7.