Unfortunately, X-HDL is a bi-directional tool and you didn't specify whether you're trying to convert VHDL to Verilog or the other way around. As far as I know, only the free version of X-HDL has size limitations, so you may want to acquire the full version of the application. However, the developer's website seems to be down at this time and I'm not sure if it's a temporary problem or one that will last, which means that currently, you can't buy the tool even if you wanted to.
In any case, there are several other alternatives available that could help you convert your project such as VHDL to Verilog RTL translator (at the bottom of the page) or vhd2vl.
