Version 5 of VMWare's x86 emulator has been released. I had recently bought version 4.5 so I was entited to a free upgrade that can be downloaded from their store. This program has come a long way since the 1.0 days and I've found it extremely useful and very easy to configure. What this program allows you to have is a "virtual" machine running within your native operating system. I can run another instance of Windows, Linux, FreeBSD, etc. inside Windows and experiment to my heart's content. If I screw up I simply delete the virtual machine file, copy over my backup (or use a feature in VMWare called snapshot) and the virtual machine is back up without me having to go through a complete reinstall of the OS and apps. A specific use I have for VMWare is to setup a work environment that if I wanted to can be shared with another simply by giving them the vmware data file. I can experient with unknown shareware in a completely isolated environment and all that other great stuff.
This all sounds great in theory but if one can't even get the VM up then it's all kinda pointless. Fortunately, this hasn't been a problem with VMWare. I was able to immediately put it to use which wasn't the case when I tried the 1.0 version. When I tried to try the 4.5 version (it's been years since I last looked at VMWare), I wondered whether it would still be the same, but it was just "worked" and I got the OS installed and went to work.
Now, performance is always a question with these type of software. The VM does run slower compared to the native OS, but it isn't that noticable (although maybe it's because I use it mainly as a development tool and don't run performance intensive apps). It probably can't run the latest video games at top speed, but for what I want to do it is excellent.
There is also a Power PC virtual machine call Pear PC which I have not tried and probably wouldn't make much sense for me to try since I don't have OS X.