how can i show a different homepage to different audience (or group) in sharepoint moss?
Redirecting to different Home page based on the User is not possible out of the Box in SharePoint. What you do is to create a Common home page and place a user control or WebPart that will detect the user logged in & redirect him to respective home page. Yes it will cause a extra redirect HTTP 303.
If the reason to have multiple home page is to show different content to the user based on the group you can always have single Page with all the webparts that display all the content and hide/show the web part that is relevant to the user.