I already have a number of files on a flash drive (8 gb) that I would prefer to keep, but I would like to try Ubuntu even if merely for the aesthetics. I use Windows XP. I know that it's definitely possible to run Ubuntu from a bootable drive like my flash drive to try Ubuntu but I would much rather keep my files intact not only on my flash drive but also my hard drive, if that's possible. I also want to know if it's entirely possible that while running Ubuntu from the USB if I can switch back to Windows while my computer is still on. If I'm missing something, please let me know. I'm very grateful for any assistance in this matter.
A live usb is like carrying a portable operating system. You can plug in , do your task. All your changes are saved (but not in live cd as cd is read only memory).But following this will damage the usb very quickly as running an OS uses large number of read and write.
You can setup your computer to duel boot with windows. In this way you can choose either operating system when your computer boots up. Once you are in one OS, you have to reboot to go to other OS. You can't change OS without rebooting.
There are two way to install ubuntu with windows xp.
Install using wubi installer. In this way ubuntu will be installed as a program in windows and you can easily remove it if require. (But remember you have to Reboot when changing OS)
The other way Defragment your C: drive.
Boot using usb or cd. Choose to install ubuntu alongside windows. Ubuntu will shrink windows partition and install ubuntu. This is bit complex task and removal is not easy.
Also You can install ubuntu in virtualbox, in this way you have to start windows, run virtual box and use ubuntu inside it. It generally require system with good processing power.
You can boot from USB without touch anything in the hardrive, but the files in the USB will be lost unless you create a second partition on it in order to save Ubuntu there away from the files.