I am that adventurous type to try to update weblabor.hu from Drupal 4.6 to Drupal 5.0 directly. This type of update is not recommended, because it is not ensured that everything will work fine. Unfortunately this time the direct update is not possible without some tweaking of the system.install files, but it seems to be doable.
The problem lies in the fact that Drupal 4.6 (and 4.7) supports only code defined node types, so there is a hook to ask modules about node types they define. That hook is called in two updates to fix variables and other changes in Drupal (between 4.6 and 4.7). For this to work correctly, one needs all modules he used in 4.6 (in 4.7) for the update script to query all node types.