Partions
 

I am using a inspiron 6000 from dell with an SDA hard disk I want to make ubuntu my main OS how do I increase it's partion size and decrease windows.

I'll probably take some heat for this answer, but the simplest, quickest, and best way is to reinstall both OS's.

Look, I can't reinstall the OS's and need an esier way where I can keep my files.

Things such as gparted are supposed to handle this, but I've never got a GUI to handle it properly.
I'd suggest you use ntfsresize from the ntfsprogs package, and reduce the NTFS. There is a very good page on the project site with plenty of info.
Rather than trying to resize the Ubuntu as well, think about creating a new partition, and mount your biggest directory there - say /media/mp3s or whatever.
Simple generally works best.

Of course, backups are the first priority.

...and by the time you've got a good back-up, you might as well re-install.

Well i've got an easier way so i'll do that. thanks anyway though!

well, qparted always did the job for me. gui working fine.