i have windows 7 and i want to boot linux from a memory stick without installing it as i would like to run 2 OSs on the same pc without losing all my files.(does anyone know how to get into the OS selection menu on a dell inspiron duo?)
What you want to do is boot the OS from your computer system's BIOS and leave your current OS untouched. That's easy.
Follow the above instructions, after it's on the USB it's now a "LiveUSB" or "bootable USB".
The OS will then be loaded, if everything is set up correctly, by BIOS and put into your computer's memory/video memory.
It will be the main OS in memory, and Windows will remain on your other media untouched.
You can also optionally do a full install of Ubuntu on a USB stick.
Okay first let me tell you that you can properly install Ubuntu along with existing windows without loosing any data!!!
i.e you can use 2 OSs properly installed!!
And about the USB boot,you will have to make a bootable USB(having the iso immage of the Linux/Ubuntu you want to install) using an application for doing so(Google it for a windows app) then you have to enter the bios setup and change the boot-order to USB as 1st boot device and save and exit.
insert the USB and restart...Linux will start.
My understanding of your question is that you want to boot on Ubuntu from a USB memory stick. Here are the steps to follow:
You are done !
If this doesn't work, maybe you have to configure your BIOS. Just follow those instructions to achieve that. If you still have problems, or if this does not answer your question, don't hesitate to edit your question with more details; it will be a pleasure to help you.
If I understand the question correctly, the thing you are worried about is losing your files when installing Ubuntu. There are three solutions to this problem:
Running from a USB stick
As this is specifically what you asked for, I will describe this method first:
There are however a few downsides to this if you're planning to use Ubuntu on a daily basis:
Installing Ubuntu inside Windows
A second method is to install Ubuntu from within Windows using Wubi. The installer will install Ubuntu alongside your existing Windows installation, so that your existing data is preserved, and you can easily uninstall it like any other application. When you start your computer, you will be able to choose if you want to boot into Ubuntu or Windows.
Installing Ubuntu normally
By default, the regular Ubuntu CD installer will repartition your hard drive in such a way that all existing data is preserved. So even if you install it this way, you won't lose your files in Windows, and you will get the option to boot into Ubuntu or Windows when you start your computer. This is very similar to installing Ubuntu inside Windows, except that you can't uninstall it as easily.