can't create srever

i'm trying to create a server, just for a few hours, to play online with a friend.
the creation of the server goes nromal, but somhow, that friend can't see my server anywhere in the list of servers...
i'm pretty new to team fortress, and this is just the first time i tried to make a server, but i hope anyone can help.
these are my computer specifics:
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System Information
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Time of this report: 7/1/2009, 11:56:22
       Machine name: WOUTERSE-C0A01A
   Operating System: Windows XP Professional (5.1, Build 2600) Service Pack 3 (2600.xpsp_sp3_qfe.090206-1316)
           Language: Dutch (Regional Setting: Dutch)
System Manufacturer: MICRO-STAR INTERNATIONAL CO.,LTD
       System Model: MS-7514
               BIOS: Default System BIOS
          Processor: Intel(R) Core(TM)2 CPU         E8500  @ 3.16GHz (2 CPUs)
             Memory: 3072MB RAM
          Page File: 817MB used, 6139MB available
        Windows Dir: C:\WINDOWS
    DirectX Version: DirectX 9.0c (4.09.0000.0904)
DX Setup Parameters: Not found
     DxDiag Version: 5.03.2600.5512 32bit Unicode

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DxDiag Notes
------------
  DirectX Files Tab: No problems found.
      Display Tab 1: No problems found.
      Display Tab 2: No problems found.
        Sound Tab 1: No problems found.
        Sound Tab 2: No problems found.
          Music Tab: No problems found.
          Input Tab: No problems found.
        Network Tab: No problems found.

--------------------
DirectX Debug Levels
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Direct3D:    0/4 (n/a)
DirectDraw:  0/4 (retail)
DirectInput: 0/5 (n/a)
DirectMusic: 0/5 (n/a)
DirectPlay:  0/9 (retail)
DirectSound: 0/5 (retail)
DirectShow:  0/6 (retail)

---------------
Display Devices
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        Card name: ATI Radeon HD 4870
     Manufacturer: ATI Technologies Inc.
        Chip type: ATI Radeon Graphics Processor (0x9440)
         DAC type: Internal DAC(400MHz)
       Device Key: Enum\PCI\VEN_1002&DEV_9440&SUBSYS_24401682&REV_00
   Display Memory: 512.0 MB
     Current Mode: 1680 x 1050 (32 bit) (60Hz)
          Monitor: Standaardbeeldscherm
  Monitor Max Res:
      Driver Name: ati2dvag.dll
   Driver Version: 6.14.0010.6962 (English)
      DDI Version: 9 (or higher)
Driver Attributes: Final Retail
 Driver Date/Size: 5/16/2009 05:38:15, 335872 bytes
      WHQL Logo'd: n/a
  WHQL Date Stamp: n/a
              VDD: n.v.t.
         Mini VDD: ati2mtag.sys
    Mini VDD Date: 5/16/2009 05:58:45, 4069888 bytes
Device Identifier: {D7B71EE2-D700-11CF-006E-4A04A1C2CB35}
        Vendor ID: 0x1002
        Device ID: 0x9440
        SubSys ID: 0x24401682
      Revision ID: 0x0000
      Revision ID: 0x0000
      Video Accel: ModeMPEG2_C ModeMPEG2_D 

I sometimes host a listen server with a friend.

In the console type sv_lan 0 then change the map.

If you have a router you may have to forward your ports.

http://portforward.com