You don't need to disconnect from your ISP. Here's Phreakdaddy's unofficial guide to getting a 200 pop single-player game.
1. Connect to the Internet. Browsers, ICQ, etc, are not needed.
2. Open AoE/RoR.
3. Select "Multiplayer."
4. Select "TCP/IP Connection."
5. Create a game.
6. Click on the slots and change as many as you want to "computer".
7. Choose civ, settings, pop limit, etc, and click in.
8. Click on the Launch button and get ready to rumble! Some notes
ˇYou must have the cd in to play. (assuming it is single player)
ˇThe computer will play as if it was still 50 pop limit unless you are playing a scenario with an .ai file made specifically to tell it to build more than the required # of houses, units, etc.