A USB port supplies 5V at a varying ampage. There's no specified way to connect this to another USB port. And no specified way to receive 5V through USB. So the result is unspecified and will probably vary. Some systems might be fine, others will have power supply problems.
Quote: "btw is it possible to do that with certain usb types, or not at all?"
There's only one type of USB. Server-client. That's the design.
Athlon64 2.7gHz->OC 3.9gHz, 31C, MSi 9500GT->OC 1gHz core/2gHz memory, 48C, 4Gb DDR2 667, 500Gb Seagate + 80Gb Maxtor + 40Gb Maxtor = 620Gb, XP Home
Air cooled, total cost £160