Reading network data being sent to another program?

[NickPaul]

This is probably going to be really hard, but I've got a month of holidays so why not waste some time. I've downloaded a piece of software that receives data from an external server. I would like to write a program that reads this data before it gets sent to the program. I'll need to do some reading up on how data travels from application to final destination.

I was just wondering if anyone could give me some tips/resources that could help me get started. Is it even possible?

Thanks,

Nick.

[Seraphimsan]

That's called a packet sniffer and that is spyware. I trust you're not using it for anything malicious, but alas I don't know any recourses or tips because of this.

[Athar]

Is there any particular reason you want to write it yourself?
There are already tools for this, such as Wireshark.