Writing code to control other web sites

Hi all

I wish to know if I can write asp .net code to open other web sites and write my code to control that site through my code. I wish to write an algorithm for something like a program trading where trades are done by the program based on logic. I have little programing expereince in asp .net and have done pages on VWD and VB 2008 express editions and use linq to sql for data access. I presume I will have to control that trading site's post back events through my code. Will I be able to do that? Any ideas will be very useful for me to start thinking on those lines.

Regards

Ticktrader
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