I would recommend staying away from running a PC and being DM at the same time. Instead, make some ally NPC's that will tag along with your player now and then, but make sure the spotlight stays on the real PC. Another good idea is to have you friend play two characters.
One on one sessions...
Beyond the Crystal Cave - Lv 1 Dungeon mag 211
The Elder Elemental Eye - D&D Encounters season 8
Killing Ground - Dungeon mag 189
Dark Heart of Mithrendain -Dungeon mag 157
These would be good starting points. Just replace some of the monsters with the ones you like.
There is a very good and helpful site - pbworks. Try and google for Scales of War. Its one of the first hits you get. I have the link but this forum won't let me post it...
I'm running a campaign as the DM for 4 players. They are currently 4th level and the group consists of two fighters, a wizard and a cleric. In our last sessions we played through the first part of Cairn of the Winter King. The session ended when the group decided to take an extended rest just...