Unauthorised attempts to logon to network

I have noticed this morning many many attempts to log onto our network from outside with made-up random user names - Lots of failure audits in the security Log.
I guess this will be someone trying to access our network but cannot shut down access as we have remote and home workers using RWW.
Is there any way i can identify the IP address so I can block it on the firewall?
Many thanks
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DaveA66Author Commented:
Sorry, below is a typica entry in the Security Log

Logon Failure:
       Reason:            Unknown user name or bad password
       User Name:      info2
       Domain:            ipofficeltd
       Logon Type:      8
       Logon Process:      IIS    
       Authentication Package:      MICROSOFT_AUTHENTICATION_PACKAGE_V1_0
       Workstation Name:      SERVER
       Caller User Name:      SERVER$
       Caller Domain:      ipofficeltd
       Caller Logon ID:      (0x0,0x3E7)
       Caller Process ID:      1640
       Transited Services:      -
       Source Network Address:      -
       Source Port:      -

Since the logon process is IIS then the IP address should be in the IIS log usually located in

You'll have more than one IIS log directory on SBS2003 named W3SVC1, W3SVC2, etc
Match the time stamp in the log with the time of the event in the security log.

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DaveA66Author Commented:
yes found it.
Someone trying to access our FTP server.
Many thanks
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