Which mail software are you using? If you use 'Outlook Express' you simply go to Tools, then down to Accounts, then Add and you should be able to work it out from there. If you are using 'Outlook' it should be a similar set up.
The problem with dusty's suggestion is that it will merge the mail from both accounts to one mailbox. You can setup different logon profiles on Windows which will allow you to setup individual Outlook Express (or Outlook) accounts for each person. If you have office and don't want to be bothered with creating profiles, setup yerself with OE and yer missus with Outlook.
Ahh wai found it. Go to file and Identities and you can setup an identity for you and your wife and then switch between the 2 without your mails getting merged. The switch option is under file too.