There are many alternatives for the asset module in Drupal 6 that make an upgrade from the Drupal 5 version redundant. A popular solution is the combination of FileField, FileField Sources and IMCE.

To migrate the files and nodes created with the asset module to Drupal 6 Eric Katz created a migration guide that converts the asset input format tags to standard HTML for documents and images.

Comments on the guide can be addressed in the issue queue.