A friend i chat to on here gave me their email address and i thought i'd stored it but i have just been looking through my contacts and it looks like i haven't :(
i have no other way of contacting them, and i have tried to remember the email address but it keeps throwing it back saying it doesn't exist ( this is because i am trying different combinations of the bits i can remember) can someone please :help: me

Have you tried PM-ing them?

Do they have contact by email enabled?

Both the above are ways of contacting your friend.

A friend i chat to on here gave me their email address and i thought i'd stored it but i have just been looking through my contacts and it looks like i haven't

Did you contact them via your email client (ie Outlook express, Thunderbird etc)? If you did then you should be able to find a copy of the e-mail you sent them in your "sent" box.
If you used Hotmail or Yahoo it may be possible to access the sent folder if you previously configured the account to keep a copy of the emails you send.