The old Entebbe terminal is currently the site of the VVIP Terminal and is not accessible to the public from the landside.
The closest you can get to it is to take the turnoff past Kitoro (just after Pearl Supermarket if coming from town) towards the "Airserv" hangars. When you come to the Airserv entrance gate, the road will branch to the right heading towards the old terminal but there will be a military checkpoint you need to sweet talk your way through to get any further than that.
If you have a ramp pass for the Airserv hangar, you can walk around on the airside to the VVIP ramp and see the terminal there. It is an interesting building and still displays the bullet holes from its adventures in days past.