I installed linux mint 14 xfce Debian and my problem
is that the screen resolution in not the rite one I
need a resolution of 1600x900 and i don't have that
type of resolution in xfce.
What can i do

Hello and welcome to LQ.

The first thing to do is to give us more information about the video hardware you use. Please post the output of

Have you found the settings area where you change the resolution yet? Also, please do what TobiSGD told you.

Cheers,
Nbiser

code:lspci
Hello again;I honestly don't no much about computers; i have a emachines old version i can see it uses a grafics by envidia,and i see AMD Athlon 64, and it is a microsoft windows xp.In the technical part I honestly
cant say much.I just love linux programs ihave nadia installed in my other pc no problem with grafic.
but when i installed the mint xfce debian version all this problem came with the package.
I have a dell monitor 23" i got it cos of poor eye sight,in the monitor reference i have the following resolution 1920x1080,1280x1024,1152x864,1024x768,800x600,640x480,
720x400.
at this moment i am using the Resolution:1152x864 in Refresh:75Hz in Rotation:Normal
cos the default of 1920x1080 the letters are extra small an icons and so on....
well my friends that is all i can honestly say. I hope that will help.and a am very
happy with the linux mint personal Thank You very much.

First Control Center and than Monitor how much options have you there .
Go for the settings that is most suitable for you and than Apply
There is also a option called Terminal .
Click on that option .
Than type lspci return and post the outcome here