I can't modify search locations to include Network Drives

Hi,

Newbie question alert!

I'm looking to include some networked drives in the indexing so that I can search them, but they aren't appearing in the "Indexed Locations" dialog box (Indexing Options and click on modify). It only shows my 2 hard drives, Outlook and Outlook Express. I've 14 drives mapped ok, according to My Computer! Any ideas how to get them to appear so that I can select some of them

Thanks,

Adrian Lester