Using a desktop AND laptop w Pro Tools 9 MP

[changeinmotion]

I need some input. I am about a year into Pro Tools, I have a couple projects going on right now. Here is my set up:

I have Pro Tools MP 9, which I run on a desktop PC using Windows 7. I have a M-Powered USB interface, and I use an OWC external hard drive for back up storing.

1st-When working on a session in Pro Tools, which I loaded from the internal HD on the PC, does the “save as” function, which I then route to the external HD work the same as a back up? My thought process is that it would save exactly the same thing on both the internal and external HD.

2nd- I am looking in to buying a laptop for typically editing-on-the-go purposes. My dilemma is: I have an old laptop that runs Windows 7, I used the CD and installed Pro Tools on the laptop, hooked up the interface and the external HD, along with the iLok USB stick that is required. Pro Tools seemed to install with no problems, but when I tried to load anything I had worked on and saved from the PC it would not load. (I don't remember what the message was, sorry about that.)

So based on all of the information, does anyone know where I may have gone wrong in the process? I don't want to go out and buy a laptop if the one I already would work and am just doing something wrong. And I also want to make sure all of the data I am saving to the external HD is saving correctly, otherwise it isn't really serving me any purpose. Am I just not saving the data to the external HD correctly? Is it worth trying on a different laptop? Is there an easier way to do this?

Please let me know what you think. If anyone needs more info I would be happy to offer anything I can answer.

Thanks a lot!