Outlook 2007 shows the total number of items in a folder on the status bar at the bottom.
When I select a group of e-mails the information on the status bar does not change.
How can I find out how many items are selected?
Use the Count Selected Items Macro That website has all the information you need to count the number of selected items in Outlook 2007.
The following code is contained in the zip-file referenced in the Quick Install. You can use the code below for review or manual installation.
I think the best you can do is create a temporary folder, move the selected emails into that folder, and see what the count is.
Then move them back again.
I just found out that if you select 5 or more items and press Enter then it shows a warning dialog which contains the number. Something like "Are you sure you want to open X items?" (the wording could be a bit different, not using English Outlook).
I can then just click "No" and they will not be opened.