Now as its for editing sound and photographs, this PC is very slow and out of date so it won't be any hardship to upgrade BUT I am using XP and Outlook express which I want to keep because I like them. I have put off getting a new PC because of this. I have no idea how I will port all my emails over
A good reason for abandoning email clients for a web-mail service IMO.
There are lots of tutorials out there for saving/transferring email between PCs and utilities to do it for you. It's actually a relatively simple thing to do, but not if you're not confident about what you're doing. With Outlook it was (almost) as simple as copying the Outlook.pst file across, but IIRC it's not quite so simple with Outlook Express - which is long dead and worth abandoning anyway.
Maybe try HERE for starters.
An Eagle for an Emperor, A Kestrel for a Knave.