One question to ask yourself is, how important is it to have C# rather than VB.NET? If you're converting a large application, perhaps you should just upgrade to VB.NET, which will be cheaper.
There are some features in VB6 with no exact equivalent in C# (the error handling, late binding etc). Ask yourself why it's worth the manual effort to convert those, when you could go to VB.NET which does support them.
And if you don't believe me (and no-one's voted for my answer, sob sob!) maybe you'll believe Francesco Balena and Dan Appleman (in a book Moving to VB.NET) who agree with me.
