As per my understanding, You have installed VMWare on Windows XP. Now you want to install Linux in VMWare for your practice purpose. I assume that, you are able to install Windows OS in VMWare and Linux on physical machine.
It is very easy to install Linux in VMware. It is just like install Windows OS on VMWare. If you have ISO of any Linux flavor, you have to just provide it to VMware as CDRom, Start New VMWare Configuration, Select ISO file as CDRom, Power on the vmware and it will start installtion process. Provide the necessary information and will install as you install on physical machine.