So you are new to a mac, but you still need to cling to Windows every now and then. Then I can recommend you get hold of VMWare Fusion. If you want to build a Windows virtual machine, it is easy enough. However, if you want to make the machine run well, there is a few things you can do.
- If you are running Windows 7 and a older version of VMWare Fusion, consider upgrading to Fusion 3. It really does improve performance a lot.
- Get more RAM. If you have less than 4GB memory, you should really get more. It is the most bang for the buck upgrade you can do for your machine.
- First up, switch off visual effects. Open up Control Panel -> System. From there select Advanced System Settings. Under performance, select Settings. Then choose "Adjust for best performance". True, you lose some of Windows 7's eye candy, but it becomes a lot speedier. If you cannot live without Aero Peek (which is great), you can at least switch off unnecessary animations.
- If you are using Windows on your Mac just for productivity software, you might want to consider switching off the sound. Easy enough - at the bottom of the VM window, right click the speaker icon and select "Disconnect Sound Card". Its easy to enable again as well.
- If you are installing Windows 7, try going for the 64 bit version. The 64 bit version of Windows 7 will enable the use of Intel's VT instruction sets which will make the VM run faster.
- If you are running Windows Vista inside a VM, you should upgrade to Windows 7. Vista is terrible inside a VM.
- You do not typically have to give Windows more than one processor. Also, it does not need more than 1 gig RAM, or 2 gig if you do more heavy duty stuff.
- If you have the option, run the virtual machine from a second disk. All the better if that disk is Firewire instead of USB. This will make everything more responsive.
- Defragment your virtual machine. Using a tool like Defraggler, defragment your VM. Then, shut down the virtual machine and clean up your VM disk. In VMWare, go to settings -> Disk and then choose "Clean Up". Do this every few weeks if possible.
There are obviously more complex methods to improve performance as well, but these are the things I found that makes the biggest improvement.

