Combine code from 2 links:
Accessing Password Protected Network Drives in Windows in C#?
A complete Impersonation Demo in C#.NET
And do folowing steps
IntPtr token;
IntPtr tokenD;
if (!NativeMethods.LogonUser(login.User, login.Domain, login.Password, LogonType.Interactive, LogonProvider.Default, out token))
throw new Win32Exception();
if (!NativeMethods.DuplicateToken(token, SecurityImpersonationLevel.Impersonation, out tokenD))
throw new Win32Exception();
ProfileInfo profileInfo = new ProfileInfo();
profileInfo.dwSize = Marshal.SizeOf(profileInfo);
profileInfo.lpUserName = login.User;
profileInfo.dwFlags = 1;
if(!NativeMethods.LoadUserProfile(tokenD, ref profileInfo))
throw new Win32Exception();
var identity = new WindowsIdentity(tokenD);
var context = identity.Impersonate();
var browser = new WebBrowser();
browser.Tag = context;
browser.Navigate(new Uri("http://www.codeproject.com"));
NativeMethods.CloseHandle(tokenD);
NativeMethods.CloseHandle(token);
NativeMethods.UnloadUserProfile(tokenD, profile.hProfile);
context.Undo();
Its old question. Maybe you have another solution? If so, please post it.