Max OS 10 memory and space problems, help

Hi, my mom's macbook doesnt work, so she asked me to post her question; Her Macbook is messed up...


James
I am in a huge pickle

Please post this for me on EE

I cant as its 'server is not receiving'.
Please email me the answer as I am not getting into EE to see the answers.

xxxxxxxxxxxxxx


Please help me. This notice has appeared

Your Mac os x startup disk hAS no more space available for application memory.

1. To avoid problems with your computer, quit any applications you are not using.
2. Closing windows and removing files from your startup disk will also help

I have a Seagate with 1.73 TB available:
Do I have to do something to get the Seagate to back up?
      - I thought it did this automatically when ever I plug it in . . . . ?

The Seagate has three things [one is a file image] in it:
      - Photos, - 4651 items [ has only half the number I have in iphoto at the moment.]
      - iPhoto Library, - with 4656 photos
      - Roslyn, Mar 10 2010 sparse bundle
            

Questions

I. iphoto, network Diagostics preview safari textedit finder openoffice printer calendar
 . . . are all in my dock
So when I quit these applications how does this help?
Surely I am still left with a no-space problem.

2. How do I rectify a no space problem?
      - I am not computer savvy, and will need step-by-step details.

3. I suspect i have several places with the same info, - like my photographs. If this is part of the problem,
how do I . . .
      - a.  find out where I have duplication,
      - b.  set about deleting duplication


Now I have a new problem!

A window says:
Your photo library is missing. Please make sure the disk containing your photo library is mounted and restart iPhoto.
a. What is "mounted"
b. What do I do for this?
      - what disk???

Thanks