Due to Windows 10 Tech Preview is not officially supported by VMware Workstation 10, you may need to do some extra steps during the installation, but in general it works very smooth and definitely can help you to experience this future version of Windows from Microsoft.
1. To install Windows 10 Tech Preview, first you need to sign up for the Tech Preview program and download the ISO from http://preview.windows.com.
2. Launch VMware Workstation 10, from the File menu, select New Virtual Machine. In the 1st step of New Virtual Machine Wizard, select Typical Install.
3. In the next step of the wizard, select Installer disk image file and point to the Windows 10 Tech Preview ISO you just downloaded. Since this Tech Preview version is not supported, it can’t be detected by the wizard. Click Next to proceed.
4. Here you can select the operating system, since Windows 8 has the similar Windows kernel as Windows 10 Tech Preview, let’s select it as the operating system. Make sure you select x64 or x86 according to the ISO you downloaded.
5. Then follow the step to finish the wizard and kick off the installation.
6. After accepting the Windows 10 Tech Preview EULA, you can select to install the OS with Custom: Install Windows only (advanced).
7. Make sure create a new partition with the unallocated disk space (size depending on how much you assigned to the virtual machine), and select this newly created partition to install the OS.
8. Follow the Windows installer instruction to begin the installation, within a few minutes, your Windows 10 Tech Preview will be ready within VMware Workstation 10.
9. The last step is to install VMware Tools, so you can do dynamic screen resizing, Unity mode and printing. From VM menu, select Install VMware Tools, and follow the steps to finish the installation.
Now you have Windows 10 Tech Preview running in VMware Workstation.
Source: Try Windows 10 Tech Preview with VMware Workstation and Fusion