I have set it up so that messages are purged from my BlackBerry 7100v after 30 days.

Does this mean that after 30 days the messages will be removed from my Outlook Inbox as well? Or is what I'm doing different to deleting.

If you have it setup for 2-way both-way synchronization (Desktop + Handheld), then yes. If you only have it setup for to syncrhonization deletions one-way (Outlook-to-Handheld), then no.

...that is my interpretation, atleast. I've never tested it out myself.

umm I took it other way actually.

I thought that it is a space/memory saving feature to keep things tidy rather than an automatic deletion tool. Maybe someone else can help!