If you are using the computer BIOS field "Asset Tag" as a means to automate the Computer Asset entry for System Number you may be finding the CMDB Task "Inventory to Asset Synchronization is not updating the System Number with your Asset Tag. There is an article that is related to this issue, however it does not tell you a resolution for it. http://www.symantec.com/docs/TECH44306
The problem is with the task using a Inventory Data Class that does not contain a value for the CMDB Data Class to use for System Number. There is a Inventory Data Class in the Inv_HW_Chassis.[Asset Tag] that does have the BIOS Asset Tag value, but the task does not use it. You will need to open a case to get a new Stored Procedure as a workaround or wait for the fix in a future release.
I am not too clear on that second part, can you please explain with more detail?
Whenever you have data that is being gathered from managed inventory and you would like it copied or mirrored onto Asset Data Classes the CMDB rules are your best option.
First write an SQL query to return the guid of the computer and te Asset Tag from the Inv_HW_Chassis table, then you can use that query in the CMDB rule and schedule it to run Daily to populate the information.