How many archives do you have?  Also, do you have a journal archive?

The webapp search isn't designed for a large scale search but it might be your only choice if you don't have DA so you would need to break the search down to a small number of archives at a time.

You would need to grant an account permission to search all archives, you can do this via EVPM.  If this is a one off thing and you have lots of time it might get you through but if this is going to be an ongoing thing you need to get DA or Clearwell.

Thank you - for this one, I'll have to use the search.asp page, and perhaps look into installing Discovery Accelerator, as I think this will come up more and more.

You mention using EVPM to grant access to the archives (I would like to use the EV Service account to do this) - I haven't used EVPM, can you provide some guidance on how to do this?

SKTAG, EVPM is nicely described in the Utilities Guide.

This might also point you in the right direction:

http://thingsilearnedtoday.net/2011/10/26/permissions/

And official TN is 

How to give permissions to an archive using Enterprise Vault Policy Manager (EVPM)

So, my question now turns to EVPM :)

If I run evpm -f "C:\permissions.ini"

Why does it request an Exchange Server name, as I am not running anything on the Exchange server, but want to add permissions to the EV Arvchives?

You know that, EVPM doesn't.

They're just standard parameters.  You need to specify an Exchange Server, and a system mailbox.