If it's the true apricot it is prunus. It seems they have many varieties.

Here is a link that might be useful: Flowers of Vietnam

I don´t believe Vietnam location could be this one as that site tells: lol.

Latitude: 102º 08' - 109º 28' east
Longitude: 8º 02' - 23º 23' north

The flower illustrated in Cactusfreak's link with the name "Yellow Apricot Flower (Hoa Mai)" looks like a species of Ochna. The common SE Asian species appears to be O. integerrima, see link below, though the number of stamens evident seems to differ in these 2 sources.

Here is a link that might be useful: Ochna integerrima

Not sure about the Latin name, but I can add a photo I took in Saigon at Tet this year. And this one was growing in a pot in front of the tour company.

Hoa Mai Saigon 2005 Tet

Yeah, I wonder what the latin name for this tree is. When I was in Vietnam I can't help but notice how all those potted Mai all a sudden begin their bloom cycles a few days before the lunar New Year. And when Vietnam biggest holiday comes rolling by, they are just choked with all those bright, exotic yellows from the flowers. One of my relative had a big potted one that had almost no leaves. Then he watered it and all a sudden new buds began to form, followed by the leaves and the flowers.

If you weren't conviced by my previous answer, try a Google search on the words 'Vietnam' and 'Ochna' together.

Thanks for all the info.
My plant does look like the ochna integerrima. I could not find a name anywhere before. But the web did have alot of pictures of it at Tet. Thanks so much for your help on this and Daai, thanks for the photos. I can't wait for it to bloom (for the lunar New Year).

Hello Toba,
I've been searching for the same plant..I've came across a site that you can order.
http://www.floraexotica.ca/Flower-MickeyMouse.htm
(New Year Flower, Yellow Ochna - Ochna integerrima)

Hope this help. Regards, Susie

The flowers on the link titled Hoa Mai Saigon 2005 Tet looks really large, or is this just the perspective? Some birds seem to like those black berries it produce. Sometimes there's seedlings growing here and there, but haven't seen any lately.