Vb.Net Package and deployment .I need help!

Hello,
I'm working in Vb.Net about 1 year.Now I try to make a setup with package and
deploment.It's working, but I have a problem.
Before starts the instalation I have to check if a file is on target machine(in a certain path)
if that file isn't then instalation stops, if that file exist I have to extract some informations(a path) from the file
and have to check if another files exist on target machine on that path.If those files doesn't exist the instalation stops,
if those files exist the will continue the instalation.After the instalation is finished, I have to search a file in directory where I install the application and in that file I have to put the path found before.All this I have to do by code.Can somebody help me?Do you have any suggestions?I will wait answers.
Thanks