Here is a nice tips from "Subramanya Veera" on VB 6.0 to VB.Net

1. Do a UML design of your whole application (if it is not available earlier)

2. Identify the functions/Subs in VB 6.0 which can be grouped as classes and components, identified in UML.
   If your team has done a better coding by following std. coding practice  then forming components can be easily done.

2. Wrap the classes by providing appropriate access specifiers which will give way for covering security aspect of your project

3. Try to fit in your application in any of the standard patterns, this may require code change.
    But the benefit you get is easy maintainance and better effort estimation. Atleast follow a 2-tier architecture

4. Once the basic steps are done, then you can start replacing the code by .Net featured code
   (like string manipulation, multi-threaeding, security protocol, delegation, remoting etc)

With Regards,

Suresh[Microsoft MVP .Net,India]