Whereas Gmail is fairly open and easy to implement into Mail.app, Hotmail is slightly more complicated if you don't have a Hotmail Plus account. Hotmail Plus offers access to your mail through Mail.app, and there is a workaround for standard Hotmail accounts, using FreePOPs.

If you have an MSN Hotmail Plus account, you can easily access your mail through Mac OS X Mail by installing the HTTP Mail Plugin.

Once installed, open mail and go to Preferences -> Accounts and create a new account with the following details:

Account Type: httpmail
Description: Hotmail (or something similar)
Email Address: example123@hotmail.com (your hotmail address)
Full Name: Your Name
Incoming Mail Server: hotmail.com
User Name: example123 (your hotmail user name)
Password: Your Hotmail Password
Outgoing Mail server: None

Close the window and Save the Account.