Since Windows 10 is a technical preview, Microsoft recommends that you avoid installing it on your primary system. Because VMware Fusion 7 provides an isolated environment, it’s an excellent choice to run the Windows 10 Technical Preview on a Mac.
To run Windows 10 Technical Preview in Fusion 7, follow these steps:
1. Sign up for the Technical Preview program and download the ISO from http://preview.windows.com.
2. Launch VMware Fusion 7 or Fusion 7 Pro. From the File menu, select New to open the installation assistant.
3. Select Install from disk or image and click Continue. In the Create a New Virtual Machine Window, Click Use another disc or disc image…
4. In the Choose a disc or disc image window, select Downloads, then select the Microsoft ISO file and click Open.
5. The Windows 10 Technical Preview is now visible in the Create a New Virtual Machine window. Click Continue.
6. In the Choose Operating System window, select Windows 8 x64. Click Continue.
7. Click Finish to name and save the virtual machine.
8. Fusion 7 will start the installation. After accepting the Windows 10 Technical Preview EULA, select install Windows 10 with Custom: Install Windows only (advanced) to create a new virtual machine.
9. Fusion will create a new partition and allocate the disk space required for the installation. Click Next.
10. Follow the Windows Installer instructions to begin the process. Windows will restart during the process.
11. To finish, install VMware Tools in the new virtual machine by selecting Virtual Machine > Install VMware Tools and follow the installation steps.
You now have the Windows 10 Technical Preview running in VMware Fusion 7.
Source: Try the Windows 10 Technical Preview with VMware Fusion