Those nice people at Microsoft have made it possible to develop xlls for no cost.
Grab a copy of Visual Studio Express C++ from here watch out some of the links seemed moffed up – if you keep getting dumped at the C# page keep searching – its not a conspiracy. Don’t be fooled, only the C++ one will do, nothing else can create the necessary native code binaries.
Download the Windows SDK that is also mentioned on that page.
Download the xll SDK from here.
Job done. Oh there is the small matter of piecing it altogether and knowing enough C/C++. Luckily those are topics for my xlls session at the Excel developer conference.
To be frank though, at this stage I’d be tempted to go directly for the Visual Studio 2008 beta2 and start coding in that (free but expires in March I think). That includes the Windows SDK (and all the latest VSTO stuff) . The real, live version of VS2008 will be released in November, ie you can buy it and use it. There is a separate launch event in Feb 2008 for some reason.
Other free xll creation options are Dev C++ a free Windows C++ developer environment. I’ve used that for non xll work and its good. You should also be able to use Eclipse, which I keep meaning to try. Any tool that can create native code dlls with the _cdecl calling convention will do fine (Delphi-yes, VB-no, .net-no)
I’ll do some more posts on creating xlls, in the coming days/weeks. This post is just so you can get hold of all the bits and bobs (for free) if you need them.