Quote from mgookin:
Of course you can use it the same as a HDD but if you want to boot from it, you have to be able to tell your BIOS to put it in sequence before the internal physical drives.
Most manuf's like Dell & HP control this and won't let you have anything other than an optical drive before a HDD but go ahead and check.
Most BIOS's on home built systems (where you bought a box, mobo, hdd's, psu, gpu, etc) will work to use a bootable usb.
And did you know that you can use flash memory as RAM with a Windows 7 system? Connect the flash memory, go to "My Computer" and right click the flash and select "Ready Boost" and it will use it as RAM. Note: Does not work with all flash memory but most.
If you're able to get your BIOS to allow you to boot from USB, you can search online for tutorials on how to configure a compact, efficient OS install on a USB.