Right now in the Mac OS I'm using the original BT mouse and Microsoft ergonomic keyboard (wired). I was wondering if I install BC, do I need to replace the mouse or will it work also with Windows XP?
As miles01110 already said, both should work fine.
Today almost any mouse is compatible with any OS, just some special features some special mice have (multiple buttons and such) are dependent on the drivers the mouse manufacturer provides. There is clearly an abundance of Windows drivers out there.