Many of you have used the "Fabulous 40 templates" that were created for Windows SharePoint Services 3.0. Some of these templates were created as site admin templates (.stp files) and some as server admin templates (.wsp files). Microsoft is not releasing new versions of these templates for SharePoint 2010 Products. Also, .stp files are deprecated and can't be used to create new sites when you upgrade to SharePoint Server 2010 or SharePoint Foundation 2010.
So, what do you do when you want to upgrade?
Sites based on these templates should upgrade, but you'll want to try out your upgrade in a test environment before you upgrade your production environment so that you can catch any potential issues. Definitely use the pre-upgrade checker to identify any issues (some people have seen problems with custom workflows or CAML-based views in the templates). However, after upgrade, you won't be able to use STP files to create new templates.
*There are issues with a few of the .wsp files after upgrade. In particular, after upgrading, some customers are unable to create new sites based on the following templates: Absence Request and Vacation Schedule Management, Call Center, Help Desk, IT Team Workspace, Knowledge Base, and Physical Asset Tracking and Management. If you have trouble using any of these templates, you can post an issue in the SharePoint 2010 – Setup, Upgrade, Administration and Operation TechNet Forum at http://social.technet.microsoft.com/Forums/en-US/sharepoint2010setup/threads, or contact Microsoft Product Support.
So, what do you do if you're using an .stp file and you want to continue using it after upgrade? You can convert the .stp file to a .wsp file manually. To do this, in Windows SharePoint Services 3.0 or Office SharePoint Server 2007, create a site based on the template, and then upgrade the site to 2010. Then, follow this procedure:
If you can't or don't want to do that, you can look to the partner community for upgraded templates. Khalil over on TechSolutions has already converted some of these templates to 2010 for you. Take a look at http://techsolutions.net/Blog/tabid/65/EntryId/17/Fab-40-Templates-for-MOSS-2010.aspx.