Upgrading to WM5 will just install the the apps that come with the Dell version of WM5 (e.g., Pocket WORD, Pocket Internet Explorer, Pocket Pocket Powerpoint - new!, etc.). Everything else you will need to manually reinstall. Take a look at the WM5 compatibility thread for some guidance:
http://www.aximsite.com/boards/showthread.php?t=98578