Having a little trouble finding and installing the first Mekpak. I think I have it downloaded as English Expansion Mech Pack1

Problem is, when I try to run the install, I get messages aborting it saying that certain files are different or can not be found.

You can find all the files you need Here.

Im trying to reinstall the game and see if that works.

I've recently reformmated my comp, so there isnt much on here.

In trying to connect with no patches on with the basic game install, I keep getting a message that says "cannot join game there may be networking problem or the server may be gone."

I think I need to address that first before the add ons.

I have Norton AntiVirus on this computer and I've already checked the windows firewall- MW4 is on the exceptions list in programs . If Norton is a problem, I dont know what to look at or disable in order to free MW.

Do you only have MW veng, or do you have black knight and mercs as well?
You are going to need the PR patches for each. install vengiance then This patch. install black knight, then This patch, And finally install merc's thenThis patch. then all you have to do is get the rest of the files from the link i gave you in my first post.
I strongly recomend disableing ANY antivirus programs while installing MW game, or patches. The same goes for playing. hope this helps.