Can I automate the writing of XMP metadata into JPEG and TIFF files?

I have written an ASP.NET 3.5 website application on behalf of an annual international photographic competition. Entrants will be uploading digital photos in either JPEG or TIFF format. Ideally, I would write entrant identity and image title information into the XMP metadata for each image immediately after upload - but so far, I have failed to find any way to do this in ASP.NET.

Thousands of images are involved, so I need to find a way to automate the metadata insertion, perhaps with some sort of script that uses a text file (extracted from the SQL Server database on my website) as the source of the metadata for a batch of images. Is this the sort of task that can be done by writing a script for Bridge CS3? Are there any scripts already in existence that I could use? I am a total beginner in this area.

I use a Win XP PC, though I have a colleague who, I think, has CS3 on his Mac (running under the Leopard OS), so scripts for either platform might be usable.

David