The other day my check engine light clicked on. I hadn't noticed anything paticularly bad in my engine or how it's been running. I had it checked out at AutoZone and they said (forgive me, lost the receipt) that "bank 1 was running lean" and it was a possible oxygen sensor problem.

I have a few questions..
1. I don't have time to get it checked out for at a least a few more days, is this really bad?
2. Is it something I can do myself, or at least with some help? or should I have a garage do it. I'm about average under the hood, but I have friends who know more.

Any help would be greatly appreciated.