How can my programs get answers and data from websites?

My Visual Basic programs need to make Web Queries. Please can you help me find a way in which the programs can open websites, enter words into the fields, press enter, and feed the results back into the program? I have been trying all day to used Yahoo Pipeline for doing this, but it only seems to work with websites optimized for RSS feeds. I also do not know how to use it to not only receive data from the Web, but to post queries into websites. Please help?