Can I create a PST file for Outlook Web Access users?

yes you can. Use either outlook or exmerge.

you can create pst using the methods mentioned by strongline but you cannot use a pst file with OWA

We are moving the client to Outlook via pop3 and need to recover thier existing mailboxes, contacts, etc..

tmcquire47, thanks for the input, I like that solution.
In this case, we're moving the client to godaddy.com's email solution.

OK.  Well, then yep, in that case you could open the user's mailbox on any computer at your office (you could add the mailbox to your profile if you first grant permissions to access their mailbox (do that in AD, give ourself or your admin account full rights to the mailbox).  Edit your profile in outlook, so from outlook go tools->email accounts->view or change-> select the exchange account, choose change->click advanced->add type the user's username->click OK all the way out).
Once the mailbox is visible in the folder list in outlook, select it, then choose file->import and export->Export->PST->make sure the user's mailbox is selected AND check the box that says include subfolders->name a destination PST-> let it process.
That could be burned to disk or sent to the user.  They can then import from it, or simple open the PST to have it accessible from outlook.

Exmerge would work too, it is nice when you are doing several exports, but it has limitations, like 2 GB file size limit, it doesn't handle exceptions well, etc.

good luck