I have managed to make sure that emails arriving to my laptop or to my desktop get "mirrored" to the other machine (did this by ticking a box saying "leave copy on server"), but it doesn't work for emails I send; if I send an email from my laptop it doesn't appear in my sent box on my desktop. I'm about to go away for a few days with my laptop and when I come back I will need to be able to see on my desktop the emails I've sent from my laptop. thanks in advance for any help.
There are several ways to achieve this but probably the most effective and clanest one is to work with you IMAP account instead of POP (I'm guessing this is what you are using). IMAP compatible clients are everywhere so are servers. If you are using Micsoroft Outlook, Outlook Express or even Windows Mail, they have this option.
IMAP allows your client to have a "live" connection between your client and your mail server. POP only allows you to retrieve your incoming mail. When you setup your IMAP connection, you "download" your mail folders (inbox folders and sent items too) and have them "live" on your computer. Also, 99% of these clients leave a copy on your hard disk so you can read your old email even when you have no connection (i.e. at the beach, away from the city).
These days, most email servers offer this service or "protocol" including Gmail and most private hosting companies (where you setup yourdomain.com). I can't speak for hotmail because I haven't use it in many many years.
There are other ways that include 3rd companies software that you can google but I haven't find one that it's truly reliable, specially since I moved to Vista, where having so many restrictions to stablish normal connection accross several computers in my network makes it kinda difficult for them to work.