VMWare Player is a freely downloadable VMWare.
Download VMWare player software and install it on your windows OS
download an image of the Ubuntu Linux Desktop version called Ubuntu from http://www.ubuntu.com/getubuntu/download
that in iso image format.
Then download VMWare configuration bundle that contains a list of files, extract those file to some folder like C:\OS\.
Then edit the file" os.vmx file and give the path of the .iso image in that file in the line like below.
ide1:0.fileName = C:\OS\ubuntu-8.10-desktop-i386.iso"
Now open the file os.vmx file using the vmware player, that will open the Ubuntu OS.
You will get a list of options in that select the option install Ubuntu without changing your current configuration of the system
Now that will start the Ubuntu OS in a window inside your windows OS.
Now you have a browser and all the applications inside the Ubuntu OS, you can start working on that.
Double click on this window/expand it to show in full screen.
To switch between the operating systems press alt+ctrl and you can work on both Windows as well as Ubuntu Linux on the same time. By default both the operating systems share half of your system RAM.