installing extra expansions

I am playing and installing NF from the client (i got the dvd for the key but dont have a dvd rom). I want to get Factions and run that as well, since that is a cd rom, however i am concerned that, with NF still not completely installed, there might be some issues. What do i need to do, if anything?

Just add the key to your account. As long as your account has both keys attached to it, your characters will have access to content in both campaigns. The game will just automatically download stuff as you go along.

How do the two mesh? If i start a new character where will he start? How do the two campaigns co exist?

It's very simple, every information about your account is kept server side. You don't even need to install the client using the CDs/DVDs, you can download it from the official website. Since you installed using the factions CD, you won't have to do that. The only thing important here are your access keys, make sure to merge them into the same account if you want your characters to be able to access both campaigns.

When you decide to start a new PvE character, you'll be asked in which campaign you want to create the character. As for traveling between two campaigns, once you get to the port city in your campaign (Kaineng Center for factions and Kamadan for nightfall) there will be quests available to take your character to the other campaign.

If you have trouble finding the quests, the wiki is your friend: www.guildwiki.org

the only thing i have installed thus far is the access key for Nightfall. I brought Factions today (i could install that from disc since it's cd unlike NF which is DVD which i can't run). I just want to make sure the world doesn't end or soemthing because i did the wrong thing or whatever. (Though i'm not normally technophobic).

As long as the client is installed, any files that didn't get installed when you started installing nf will be download to your computer when you open the game again. The only thing you have to worry about is merging your 2 access keys. If your account is already created, on the login screen click on the Create new account or add access key link. Fro there make sure you choose add an acces key to an existing account.