Check Engine Light On

[skileptic]

I just recently bought a new 1995 S14 and my check engine light is on he said it was probably the o2 sensor or the timing. I need to smog it by the end of december so i would like to know how to turn the check engine light. They told me by disconnecting the terminals on the battery, didn't work. If I do get the check engine light off do you think i'll get problems later on? Thanks Appreciate the help.

-Roberto