If you don't want the archive pages to display, try this.
Go into the vb admin control panel.
Click on vbulletin options on the left, this expands a menu - click on vbulletin options under there.
Click on Search Engine Friendly Archive (it's near the end).
The first option should turn off the archive.
The second option may be what you're after - it turns off the "simple view" on archived threads.
But archived threads probably use a lot less bandwidth, so if you change anything, keep an eye on your stats.
