We shall probably need a few more details.

Which Operating System do you have? Which version of Outlook Express do you have? Why do you want to re-install it?

Outlook Express and Internet Explorer are normally bundled with the Operating System with branded versions supplied by your ISP's connection disk. You can usually un-install the latter by going to Control Panel|Add/remove Programmes, Scroll down the list,highlight and click un-install. You can then re-install if you have the disk or download from the web.

However this is all very drastic and you could loose all your personal e-mails.

Once, during Prohibition, I was forced to live on nothing but food and water.
- W.C. Fields
.