I had a road crank on my Gary Fisher single speed for a while. It needed a really long bottom bracket to clear, something like 122mm IIRC. And even then I had to crimp in the left chainstay a bit.

If this is an x-mart level bike I would not spend any money on it, you can get a quality project bike on craigslist/garage sale/whatever for the cost of the parts to turn your bike into a single speed. Find another bike and piece the two together into one good bike.