Webclient object to access a page login

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VB

How can I login to a website using a webclient object in VB.Net. Does anyone have tried this before? Please will you share some of the techniques? Thanks

What I have tried:

<br />
Dim wclient As New WebClient<br />
Dim loginInfo As New Specialized.NameValueCollection<br />
loginInfo.Add("username", "guest")<br />
loginInfo.Add("password", "sample123")<br />
wclient.UploadValues("<thesitehere>", "POST", loginInfo)<br />
<br />
Dim pagesource as String = client.DownloadString(<"I want navigate to some pages of the site, so I put the link here>")

but still I get the page source of the login part of the site.