You'll also be able to install inside a virtual machine like virtual box http://www.virtualbox.org/ inside your existing operating system, although virtual machines aren't as good as the real thing ( a native install ).
There's other installation methods but they're much more advanced. A USB install is the easiest way to install besides having a cd or dvd.
I think he's asking specifically about installing linux on his Sony Playstation 3 without using the Blu-ray drive. I'm not sure of the answer, but I can't say I remember ever seeing any option to boot off of USB or hdd within the PS3 ui.