James,

It would depend on how many macs and how much you sell your software for. If it is one mac and the profit off one sell is not that much you need another customer. However if your profit is worth to you and there is more than one mac user you might look into Citrix MetaFrame product. That will allow the mac user to run the program through a client on the mac. The program actually runs on the NT/Win2k server. This will allow your current software to run without a converson or recompile.