A lot of answers on low level calls/networking can be found at:

visualbasic.about.com or
www.vb-world.net

when running tcp/ip tou might want to try the free asptear.dll it supports
user id' s and passwords.
it is on http://www.alphasierrapapa.com/iisdev/components/asptear
I'm not sure if it will work in a vb app, but it's worth a look

greetz,
John