there are diffrent BSP formats (eg. HL vs Q3). Depending on the BSP Compiler tools that where used to create the BSP Map, it may or may not be legal to use it commercially. Blitz can only load Quake 3 BSPs, and AFAIK all BSP-Compilers for Q3-Maps require an Engine License to be used commercially. So for us it means: no, it isn't legal unless you'll never release it commercially, which is likely with your very first trials.
There are also some tools that will convert several BSP Formats to B3D, WRL or 3DS etc. (Although in theory it will still be illegal to use it commercially, it will be hard to proof what tools where used to create it).
There is an alternative Q3 BSP Compiler, but Bob3D told me it isn't working. Its name is "OpenBSP" and it's an open source project.
There are also some tools that will convert several BSP Formats to B3D, WRL or 3DS etc. (Although in theory it will still be illegal to use it commercially, it will be hard to proof what tools where used to create it).
There is an alternative Q3 BSP Compiler, but Bob3D told me it isn't working. Its name is "OpenBSP" and it's an open source project.