Can I debug vs 2003 code from vs 2005?

Question

I'm developing a library in vs 2003 because the tool it's for is .NET 1.1. I've been instructed to use vs 2005 unit testing to test the library, but I'm having trouble attaching the 2003 process to the 2005 test project. The tests run, and the functions are called, but when I get an error there is no way to debug the 2003 code. Is it possible to debug the library from 2005 or should I try other unit testing tools (N-Unit)?