problem in using webservice through an ISA proxy server

Hi,

I am accessing webservice through an ISA  proxy server using basic and integrated authentication.

This is the code i am using.

Dim Result As New Validatekey.Validation
Result.Url = "http://venus/Validation.asmx"

Dim mproXy As WebProxy
mproXy = New WebProxy("http://inet:8080, True)
mproXy.Credentials = New System.Net.NetworkCredential("anish","anish","inetwork")
Result.Proxy = mproXy
dim abc=Result.keyValidate()

Result.keyValidate() is a webservice call which returns a result.

This works fine. but if i change the line below

mproXy = New WebProxy("http://inet:8080, True)
to
mproXy = New WebProxy("http://192.168.0.1:8080, True)

it gives the following error
==============================================================================
The request failed with HTTP status 407: Proxy Authentication Required (The ISA Server requires authorization to fulfill the request. Access to Web Proxy service is denied. ).
==============================================================================

Only thing i am changins is passing ip address of the proxy server instead of proxy server name.

Guys please help.