If you use IMAP instead of POP3, whatever happens on one computer happens on others.
Once an account is set up with POP3, most email clients wont let you change it to IMAP. The IMAP account would have to be created from scratch.
IMAP is slow and can be unreliable. A better solution would be to move your email to a cloud based solution like Google Apps.
We are a google apps re-seller and we would be able to assist setting this up for you.