Hi,
You'll need to go to the Form Library Settings > Advanced settings, and set the library to use Content Types. You'll publish your forms via admin deploy, activate them to your site via Central Admin, and then add the Content Types to your form library (under Form library settings as well). Each Content Type (form) will show as a menu item under "New".
Microsoft should have some articles on this, but the exact links depend on whether you're on MOSS 2007 or SharePoint 2010. Anyway, Google might return some good tutorials.
Good luck!