Is there any comparation of the bandwidth usage, it seems that vnc take much more bandwitdh, but I am not sure.
Is there any way I can make vnc use less bandwidth.
You're absolutely right in your observation that, typically, VNC requires more bandwidth than RDP.
VNC is a "bandwidth hog" because it's oriented at duplicating the pixels of the remote display. Conversely, RDP is based on drawing primitives (boxes, lines, etc) rather than sending pixel updates. Think of it like this: In VNC, the pixels on the display that change get sent over the wire (simplified somewhat). If lots of pixels get modified-- say in drawing a large box in the middle of the screen, a potentially large number of pixels are modified and need to be sent over the wire. In RDP, the instruction "draw a box in the middle of the screen" gets sent over the wire (which is much more concise than a list of pixels to change) and the client "draws the box". (I'm radically simplifying this and not considering VNC compression at all, but this gives you a general idea of how it works.)
You can use various "flavors" of VNC that have different compression options, but at the end of the day the RDP protocol (and protocols like it-- ICA, X, etc) are very difficult to "beat" because, fundamentally, they need to move less data to accomplish the same effect.
Like Evan says, sending the instructions to the remote display is better than sending the picture detail.
However, I think that some advantage comes from TightVNC and UltraVNC techniques when you consider that the resolution you want to use at the other end may not be really very high.
The VNC tools allow JPEG compression and even 8-bit pixel communication that will 'corrode' the picture to some extent but give you lower bandwidth utilization and effectively speed.
You have to remember that JPEG compression is fast on computers today.
TightVNC has three connection profiles, try the Low Bandwidth option.
Also change the theme on the remote PC to be as simple as possible, no backgrounds, no gradients, etc. VNC does compress the data, and solid screen areas compress much better than pictures and/or gradients.