You might want to consider Open Office or the more Mac friendly variant, NeoOffice, both of which are free. These support Basic language macros. The version of Basic will no doubt have some differences from what Microsoft used, but should be convertible without too much grief.
Some of the early versions of NeoOffice had a very clunky user interface, but the last couple of major releases have been quite decent. I don't imagine I'll ever go back to MS Office.
http://www.neooffice.org/neojava/en/index.php
