Increasing Hard drive space / premmisions

Hi, I have a few problems i figured someone here could help me out with
First I have an hp laptop, my C drive can hold up to 80gb, and since it's hp, i have another drive called "Data" and it can hold up to 93gb. the thing is that the data drive is almost completely empty. I'm wondering if I can somehow change it so the data drive space is lower and the c drive space is higher?
If so, is there a program i need to do so?

Another problem i'm having is accessing my Documents and Settings folder. Ever since I upgraded to vista the computer tells me that I do no have permission to view that folder.... huh? I'm the admin and the only acount on this computer, how can this be solved?

Thanks in advance!!