First of all, remember to Use Unicode when practical :)  Sometimes older applications don't allow Unicode, although they usually then don't allow Microsoft code pages as well (usually being ASCII or Latin-1, which are different).

But when you do have a question about how Microsoft's "ANSI" (They're not really ANSI) code pages behave, there are a few places you can look.  Unicode has a mapping on their server at http://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WindowsBestFit/ of the Microsoft "ANSI" code pages.  They're also mentioned on the Microsoft globaldev http://www.microsoft.com/globaldev/reference/cphome.mspx site, and in Appendix H of Developing International Software.