I would just keep your 40 gig as the primary drive and make your other drive the secondary... you won't see any speed increase unless the old drive is 5400 rpm and the new drive in 7200 rpm. If they are both 7200 rpm then just add the new one.
As far as the pagefile.. I've put it on the primary, secondary and on its own drive and I haven't found that its made a difference at all.. so in my opinion just put it where ever you think you want it to be.