You'll be ok to drive with it. BUT you're going to get terrible gas mileage (if you weren't already) and no performance. You can get them lots of places online. Just browse for a good price.
The 02 sesor reads the exaust gases coming out of exaust valves to detect proper combustion. The second one might me an after-cat O2 sensor and let the system know when the cat isn't functioning properly.
Kevin (President TBEA)
"WAAAAAAARRRRRIORS, come out to plaaaaay."