Now this is cool... Andrew Troelsen's book "COM and .NET Interoperability" is FREE in e-book format at apress.com (click on Free E-Books under one of the headings). I highly recommend this book to anyone who wants to either continue to use their current COM components in the .NET world or for people who want to use their .NET abilities in COM-based technologies.
Many times I hear people say they would have to need for this. Well, let me give you some ideas of what I do at the office. Every now and again the web developer at the office will get overloaded with work and it will bubble up to the architect (me!) Well... the older websites are all in classic ASP and while I spend my share of time in the trenches with classic web application development, there is NO way I'm going to do any VBScript development. (heck, even back then I did most of my work in PerlScript!)
My solution is simple: .NET to COM interop. Most of my work is done in .NET and I just expose the interfaces to COM. You really think I'm going to consume a web service with manual XML structures in VBScript? Uh... think again.
By the way, for those web services I consume and expose to COM I wrote my own web service consuming framework (because so many people expose COMPLETELY INVALID services to the world in pseudo-"SOAP" that .NET won't get near it). I then expose these new "services" to the COM world via component services. Oh yes, the book has an entire chapter just on serviced components (COM+ Interop).