First of all, if some words may seem to be not very appropriate, then it is because of my poor english and limited knowledge of writing Dhamma in english.
As some people here already said there is a hugh differences between Buddha and Arahant. But there are also similarities here.
The similarities are both Buddha and Arahant will both go to Nirvana when they die. There are many answers here i have read few of them and i won't repeat those.
The differences are-
Buddha could become Arahant in his earlier lives but Buddha ( i am saying to the particular Buddha, Siddhattha Gotama) made a wish to become Buddha and fillfuling his Parami (Pāramitā) for 4 thinchy
and a million world to become buddha. (someone pls help me to choose better word)
Normally, a person can become a noble state and will be in Nirvana no more than 7 life times with corrent practice and enough Parami from past lives. Yes I am talking about 4 stages of realization which are Sotapanna, sakadagami, anagami and Arahant. But if a person made a firm wish to become a Buddha, he don't become Sotapanna or sakadagami or anagami or arahant, he will just filful his Parami until he finally become a Buddha. The main reason is to save the world (i mean human, animal and all other heaven or spirtual beings). But of course, not everyone who made a wish to become Buddha will become Buddha.
Arahant is someone who follow and practice Buddha's teaching and get enlightenment. There are also Passacca buddha who are also Arahant but they get enlightened without a Buddha's teaching. There can be no Passacca buddha in the time of a Buddha.
Here is a monk who got enlightened and died as a Arahant about 50 years ago. Please refer to the following link. http://www.dhammadownload.com/MogokSayadaw-mp3.htm
Sorry guys, it's just in Burmese not in english. But I could translate more about that, if anyone wants to know. I also want to know more about Arahant if there are any others in near past.
Hope my answer will add to others and helpful as well.
With Metta, Laurence.