Ukraine is a deeply divided country. The western parts are mostly eastern rite Catholic with many ties to Poland and the West. The eastern part is more Orthodox and Russian and is oriented towards Russia.
Yushchenko was the candidate of the western part of Ukraine, while Yanukovych has his support in the east.
Here's a map from parliamentary (the Ukranian parliament is called the Rada) election voting trends in 1996 indicating general opposition to leftist policies. Note the concentration of the opposition to the western parts of Ukraine. 