How many url rewriting rules can be added?

[xin]

I am using Urlrewriting.Net, it's nice tool, it does as expected till there are more than one site under root. With one site under / works fine, however as soon as there is another site added under / , the rewriting rule got applied to that site as well. So my question is how many url rewriting rules can be added to umbraco, and if it's possible to add more than one, how do these rules get interpreted? I mean which rule comes first, and which rule comes last.