I've read a lot here (and in the official books) about balanced parties in Dungeons and Dragon's 4th edition. Parties should contain at least one each of four specific roles, a distribution of skills (for checks), and character-levels all assumed to within a very narrow range, say + or - 1 from the average.
As a AD&D first edition game master, I find this all rather intimidating.
Back then, other than making sure they had a healer, I never determined "combat roles", never made sure they always had an even distribution of anything - money, magic items, or even levels. It wasn't unusual for there to be a 2, 3, 4 or even 5 level difference between the lowest and highest in a group. The experience point distribution tended to advance those behind quicker, so it didn't seem like a big deal and tended to self-correct. Perhaps as a DM I was compensating for weakness in monster tactics, but it wasn't obvious, even to me.
Can D&D 4e be played the same way? What, happens when there is a friendly "overpowered" character in a group? When does the difference in level (and consummate abilities) become untenable for the DM? for players?
I've got some higher-level NPC/Allies as story-arc characters in my new campaign, and they will do some fighting side-by-side with the party, so experienced guidance would really help me out...