I don't have access to running any installer at the minute so I knew that if running from the CD you just burn the iso file to the CD and your ready to go..but can I download this iso file to my USB and run it straight away when I change my bios to boot from USB?..or do I have to use the installer?..I can't use the installer for different reasons and I'm not really looking to install ubuntu just yet I just want to run it off my USB to try it out..so is it possible not to use the installer to put it on my USB? (I downloaded Ubuntu 12.10)
The answer is yes and no.
No you cannot just copy the file to a usb and have it run, it will be missing important files to allow the boot. You could burn the ISO directly to a DVD(instructions HERE) and boot from the DVD(a CD is too small for 12.10 but can be used for 12.04)
You can, however use a program to install it ISO file onto the USB so that it can be booted.
The instructions to make a bootable USB in Windows are HERE. You can then use the USB stick to try Ubuntu.
Note: Using either the LiveDVD or the LiveUSB will allow you to try out Ubuntu and check to see if you like it and that it will support your hardware but the speed will be considerably slower. The LiveUSB will be faster than the LiveDVD but still slower than a full install.
When you boot from the LiveUSB you will be presented with a menu, just select Try Ubuntu and it will boot into a fully functional (but slower) Ubuntu environment.