I have a Debian Linux installed as a VMWare guest.
I want to create an .iso (or .img) from this installation, from which I can create a server installation.
How can I achieve this?
The way I've always done this is just the same way I backup my real world Linux partitions. Linux has dozens of ways to do this but you'll want something which is capable of restoring to different hardware (so anything which does an EXACT disk image isn't going to work). One solution which will is:
If you want to use clonezilla, here is a tutorial: http://www.dedoimedo.com/computers/clonezilla.html
It basically works exactly the same in a VM as it does on a physical machine. You'll need to mount the image to your VM using the hardware setup screen in VMWare to simulate having a boot disk in at bootup.
To use an image file in the virtual machine, follow these steps: