Hard Drive Problem

I have a mid-2009 white MacBook. I would love to buy a bigger, better machine. For now, I have no other options because the LED screens on the newer machines hurt my eyes. You can read about that here if you are interested. https://discussions.apple.com/thread/1677617?start=0&tstart=0 I just want you to know how desperate I am to keep this machine.

I use my computer primarily for documents and recently started downloading television programs to watch on my iPod. This morning I received an error message that said my start up disc was full. ?? Also, while trying to download a season of a show onto my computer, it stopped and said the destination disc was full.

I looked at About this Mac and saw that I only had 32MB of space left. 😮 I emptied my trash as directed, and deleted some TV programs, but still now I only have 31.38 GB of my 159.7 GB capacity.

I did Get Info for what I thought were the big folders on my computer and this is what I found.

15GB of photos

1.59 GB of documents

9GB of applications

67GB itunes (24GB tv shows) (13GB music) not sure what's taking up the rest of itunes 67GB?

I was shocked that the programs (Non-HD) took up so much space.

My questions:

1) How can I find out what else is taking up so much valuable space?

2) Can I have a larger harddrive installed on this computer?

3) If so, what are the negative implications of doing that?

4) Less than 32 GB of 159 is not very much is it?

5) What else is taking up space on iTunes? I only have music and those TV shows. No movies.

I have used Macs for about 8 years, but I am not very savvy about the workings of the computer. Thank you for any help/advice you can offer. I appreciate your time.