I am going to attach an IDE drive to a new pc using a external dock
1)Will I be able to delete windows xp which is on the ide drive to make space ?
2)As I understand it I will not be able to use software from the old drive when it is attached externally to the new pc?
3)I will be able to access files such as word docs, pictures etc (as long as I have the software to run them
It is unlikely that any software will be useable unless, as Fruit Bat says, it is standalone (typically standalone software would not have been installed using an installer). The vast majority of software is not standalone, so unless you know otherwise, I think you should assume software is not standalone.
Best course of action (including to eradicate XP) is to copy everything you want off the drive (e.g. on to your main drive). Then format the external drive and copy back whatever you want to put on the external drive.