I have BT5 as my OS. Things that I haven't figured out are how to download Skype and how to use my webcam not to take picture but to use it with Google talk and/or Skype. Does anyone have an answer? Thanks in advance.

If you are going to use BT5 as your OS, make sure you create a regular user account. BT5 is designed as a pen testing OS and not really meant to be an "everyday use" OS (however it can be I guess) but the default user is the root user. Big security no no if you are running as root all the time.

Anyway to answer your question, you can download skype here: skype download and select the ubuntu version from the drop down either 32 or 64 bit depending on what your running. The skype software should take care of your camera setup. (I have not tried the new skype 2.2 beta, however support on linux is not near as good as other OS's so you may still have some trouble)

I've been using BT5 for exploitation purpose but now I'm trying to use it just with skype. Do you know how can I go back and change from root user? Thanks again.

First you need to create a new user (with useradd) and then you need to go to the configuration of your login manager and deactivate the autologin for root. Don't forget to add your user to the needed groups, in order to have audio etc.
At least that's what I did on my bt3. Of course you can't perform the pen tests from your regular user account since most of them require root access. I used bt3 for everyday tasks on my acer aspire one for 2-3 years, untill I switched to gentoo recently.
Hope I helped a bit.