First question of what might be many.

I am taking delivery of a new camera today, I've got a 400D currently. Because I am not very computer literate, I downloaded all the discs that came with it, zoom browser, DPP, Picture style editor (which I dont use) and EOS utility. My question is, I assume I will be getting all newer versions of these programs when I get my new camera today. I think I'd have to keep the 400D's zoom browser cause that's where all the photos I've taken with it are stored (I think) but can I safely delete/uninstall all the others and still use the new ones on my old camera as well.

Yes. The newer versions tend to support older cameras. Your 400D isn't that old, so I expect it would still work with the newer software.

Thankyou for your quick response! Would it be worth my while transferring all my 400D files to the new zoom browser and uninstalling the old one as well, I dont even know if that's possible.