In TP9 you select the images and then use
Image | Batch Edit Metadata.
In this case, to write the database keywords to IPTC keywords, you enter:
[*]FIELD:
Keywords[*]OPERATION:
Set (or
Append if you don't want to overwrite any existing IPTC keywords)
[*]FROM:
Image Info > Keywords[/list]
Then press Add, and the operation will be put on the operation list. The operation list (or 'batch') is what will be performed when you press OK. You can save this list for future re-use.