First of all, I would like to apologize for not seeing the reply in March.
Secondly, I would like to thank Prophet for the very interesting post and recommendation to install the SP.
I'm not sure why SharePoint 2010 browser forms do not read/display attachment fields saved in 2007 but it could have something to do with the object model change and the fact that the forms use code. That doesn't make a lot of sense, and is just the only wild guess I have ...
One possible workaround (if the Service Pack doesn't fix it) is to convert the attachments into links to files stored in a document library. This can be done in a batch way and would result in the added advantage that users can edit the attachments without having to open the forms (or maybe that's a disadvantage if you want to control edits).
At any rate, we do have tools (qRules and Doc Deployer) that can help to create this workaround. Free trials exist. qRules and Doc Deployer can be installed for free but the script to convert the files will likely take a couple hours of our time (one support incident).
That's the only option I can think of for now.