For all the user databases and model,msdb you need not stop the services. Its just a normal restore. But inorder to restore the master database you need to start Sql server in single user mode and then perform the restoration.
For your scenario if your server goes down you need to perform the following,
1. Reinstall Sql Server 2005 and apply all the service packs as it was before.
PS: You need to have the same build and same edition of Sql Server 2005 to restore the system databases.
eg.) if your full backup was taken when you were using Sql 2005 SP2 with cumulative hotfix 2 you need to reinstall Sql 2005 SP2 cumulative hoptfix 2 to perform the restoration.
Refer this KB for more info, http://support.microsoft.com/kb/264474
2. Restore all the user databases from most recent full backup
3. Restore msdb and model from the most recent full backup
4. Stop Sql Server and start it in single user mode and restore the master database. Refer Step 5 alone from this link for more info, http://sql-articles.com/index.php?page=articles/rebuildsysdb.html
5. The users will be there once you restore the user databases and the logins will be available once you restore the master database.
6. There might be mismatched ids when you restore any database and in that case you need to make use of sp_change_users_login stored procedure to fix the same.