What is the best way to move old data from X database to new application in automatic mode? How to call HTTP GET and HTTP POST requests from C# code?

Hi,
How can we call HTTP GET and HTTP POST requests from C# code?  I want to move data from old database to new application through C# code in auto mode.
setps that I Wanted to do(through C# code):
1) Get login page using HTTP GET(C# code) and call HTTP POST(C# code) with username and password
2) Get profile page(using HTTP GET) and call HTTP POST  to post different profile fields to server (C# code)
3) Get next subprofile page(using HTTP GET) and call HTTP POST to post different sub-profile fields to server

What is the best way to move old data from X database to new application in automatic mode(instead of manually entering all records)?
Note:  We don't have access information about new application database. Can we mimic new application's POST form request and call same type of request from C# code(using HTTP Post)?