One of the comments to this blog today was asking about how to push custom field data from LEAD into CONTACT or ACCOUNT once the lead is converted to a prospect.
To do this using CRM Customization, you drill down into the specific RELATIONSHIP within the entity (in this case LEAD to ACCOUNT) and then you can add a MAPPING that maps a custom field in the LEAD to a similarly designed custom field in the ACCOUNT. This map pushes data from one to the other when the Account is created. It is not ideal and can be supplemented with some workflow (for instance if the account already exists), but it is similar to how the current system fields are being populated during convert.
If you are still unsure as to how to approach this make sure you talk with your Dynamics CRM partner technical specialist. There is SO much that can be learned and mastered within Dynamics CRM! Tap into all that experience that surrounds you!