I want to use 25gb for the entire install.
That's barely enough for the root partition. 30GB is better. But neither allows you much room for adding programs and
storing data files.
So swap would be 2gb? What about root & ext?
As a general rule of thumb, swap size should be twice the size of available RAM. However, for burning large DVDs and some multimedia tasks, swap should be at least 4GB. / is the root of the Linux filesystem. /root is the user root's home directory. Two different concepts. Define what "ext" means.
Also if I delete the partitions will I need to fix the windows mbr first or just continue with a fresh install? Will it repair grub?
That depends on what is already written. There are lots of questions, but very little usable info to go on. Boot from a PCLinuxOS live CD. Open a terminal, and enter:su
Post the output shown right after fdisk [space] (dash) (lowercase L).