First you need the installation ISO. Tell VMWare to create a new virtual machine, mount the ISO ans then start the VM. From there, it is just like installing on a regular PC. Though after you complete the installation, you should install the VMWare client tools.
Alternative: download a vmware VM that alreayd has Ubuntu install - google should turn up some places to download one.
There are basically 2 ways to get Linux running in a VMWare VM. One is to download, install, and boot an "appliance VM" that's already configured and ready to run. I have a Wikimedia VM that I got this way, and have constructed 2 appliance VMs of my own; a mail services VM with sendmail, dovecot and mailman in it, and a development support VM with SVN and Trac in it. VMWare has a gallery of such appliance VMs, I think, and Google can turn up other sources.
The other way to get a Linux VM up and running is to build it from scratch. Allocate a virtual hard drive (5 GB is usually good for a basic OS), construct a virtual machine from whichever VMware "control panel" you are using, attach a virtual CD-ROM/DVD to boot off of (or you can do a network-based install if you are up to it) and boot off of the virtual CD-ROM (which can be representing a physical CD/DVD or an iso file).
About the only other major consideration is how to configure the virtual network. You have 3 options. VMWare allows a VM to own one or more fixed IP addresses, forward certain ports from the VM host, or run an IP masquerade.
An IDE is no substitute for an Intelligent Developer.