Have a look at VMWare vCenter Converter ( http://www.vmware.com/products/converter/ ), which will convert a physical machine to a VMWare virtual machine. This can be run on VMWare Player, which is a free download.
This reply seems to cover what you want, if you need a bit of assistance executing the commands noted (e.g. you don't know what a livecd is, are unsure of what dd is, etc.) stop on back and we can help
Be sure to test your VM thoroughly. The last product I supported was not officially supported in a VM, although on the helpdesk we would always try our best to help. From an extensive number of clients we found that those that installed the OS and our application into a clean environment had no issues, those that sucked up an existing physical box to create the VM could never get our product to work. This was using the VMware converter tool. As we didn't offer any official support I never had time or funding to really get to the bottom of it other than it was an interbase engine issue.
Personally I'd build from scratch inside the VM where possible.