Hi,
I am going to assume you need to do this because you are trying to install Linux on a netbook that does not have a CD/DVD drive. The .iso file supplied by the websites is an image file that is not suitable for installation by just copying it to your flash drive. A little more work is required.
You need to download a free program called "Unetbootin" (available for Windows or Linux) that will take the .iso file you have and create a bootable installation version on your USB drive. With Ubuntu or Mint, you have the option of running in the "Live" mode which does not permanently install the software, or you can double click the "install" icon to install Linux on your hard drive. When you create the bootable USB drive, it can only have one OS on it at a time. --you can't install both on one USB drive. The default installation for Linux Mint 10 will reduce your existing Windows partition to about 50% and install the main Linux partiition and smaller Swap partition in the remaining space. When you start the computer, a screen will allow you to choose between the Windows and Linux OS's and their respective recovery boot options.
You don't want to overwrite Windows unless you are really into Linux (my family has been using Linux for 8 years and we've never had any malware infections even without ever having use anti-virus programs). We don't use Windows.
Here's the link for the "Unetbootin" program download: http://unetbootin.sourceforge.net/
UNetbootin allows you to create bootable Live USB drives for Ubuntu, Fedora, and other Linux distributions without burning a CD. It runs on both Windows and Linux. You can either let UNetbootin download one of the many distributions supported out-of-the-box for you, or supply your own Linux .iso file if you've already downloaded one or your preferred distribution isn't on the list.
Requirements
Microsoft Windows 2000/XP/Vista/7, or Linux.
Internet access for downloading a distribution to install, or a pre-downloaded ISO file
Features
UNetbootin can create a bootable Live USB drive, or it can make a "frugal install" on your local hard disk if you don't have a USB drive. It loads distributions either by downloading a ISO (CD image) files for you, or by using an ISO file you've already downloaded.
Once you create the bootable USB drive, you will probably have to get into your boot options BIOS on your computer and select the USB as your first bootable device.
The current Linux Mint has a feature to automatically create a bootable installation USB drive for you. (But you have to have a working copy of Mint ver. 10 or ver. 9).
Just go to Menu > Control Center > Hardware > Startup Disk Creator and you can create your bootable USB drive. This is handy if you have a Linux Mint desktop and want to easily create the Bootable USB drive for your new netbook.
I hope this helps.
Joe