How do I handle animosity from a co-worker? I think it's jealousy over a promotion... PLEASE HELP!?

I work in a small office of an installment company and the total amount of people in our clerical staff is about 30. Out of those only about 10 of us sit in a cubicle... and with things changing around the office, I received one of two lead positions. This [person] I'm asking about how to deal with, did not get any of the lead positions. Leads are the only ones with steady times for work, most everyone else rotates... and worst of all [or I least I think it's worse] this [person] will be working for me most days according to our schedule 'til the end of March.