eWallet's installation software will install the application into your Mac's global Applications folder - that's the Applications folder that your Finder window has a shortcut to, and which you will see at the top level when you open your Mac's hard drive in the Finder.
In order to do that, it has to ask you for an adminstrator password (your user account password if your account is an administrator, or the username and password for a separate administrator account if your account is a limited user.) If you are familiar with Windows Vista and Windows 7, it's the same thing as Windows asking you to approve the installation with a User Account Control elevation prompt that darkens your screen.
This is completely normal and does not indicate that eWallet is attempting to modify important system files. eWallet's installation process does not install any files into your Mac's /System folder. It installs the application into /Applications, while the sample wallet, preferences, and some application support files go into your user account at /Users/YourUsername.
If you don't want eWallet installed to the global Applications folder (/Applications), allow the install to place the application there and move it to your user-only Applications (/Users/YourUsername/Applications).