Thanks for the answer, thats the route I was investigating but unfortunately I haven't found a way to make it work for Document Libraries - only Lists.
The problem I have come across is that aving a SPUtility.Redirect in the ItemAdded, ItemAdding, ItemCheckingIn or ItemCheckedIn event on the document library doesn't do anything at all, because there is no page related to the events - its all backend code being fired that is not linked to a web context, because its not the webpage doing the heavy lifting at that point but the Office integration.
All of the examples I have come across seem to rely on the fact that the EditForm.aspx or NewForm.aspx page is being displayed at the time the event is fired, which of course is not the case here.
This also leads to the problem that I cannot extend the EditForm.aspx or the CheckIn.aspx page to do what I want either, because Office 2007 circumvents both of these.
So, the only option left open to me at the moment is doing it through a workflow :/
Any further tips would be fantastic.