T-SQL to perform a specialized INSERT INTO

I'm not too familiar with T-SQL and was wondering if I could get some help with an INSERT INTO statement..  

I have two tables, tblAssets and tblADComputers.  I am writing a job that creates entries in tblAssets for every computer in tblADComputers where my FK in tblAssets is set to tblADComputers.objectGUID

I understand you can do an INSERT INTO tblAssets (<fields>) SELECT <fields> FROM tblADComputers but there are a couple required fields for the new tblAssets entries that I need to set in the statement as well..  So I was hoping to make it look something like

INSERT INTO tblAssets (field1,field2) (field1value, (SELECT <field2> FROM tblADComputers))

Is this feasible?

Additionally, I don't want it to attempt to create duplicate entries, so if the objectGUID FK already exists in tblAssets, I don't want it to attempt to reinsert that objectGUID entry from tblADComputers.. I assume this would include some sort of WHERE NOT EXISTS clause but Im not sure how to put it together.  Any help with this would be greatly appreciated.