INT3 breakpoints are briefly explained here.
int Manualbreakpoint(ulong addr,int key,int shiftkey,ulong nametype,int font);
void Tempbreakpoint(ulong addr,int mode);
int Setbreakpoint(ulong addr,ulong type,uchar cmd);
int Setbreakpointext(ulong addr,ulong type,uchar cmd,ulong passcount);
ulong Getbreakpointtypecount(ulong addr,ulong *passcount);
int Setmembreakpoint(int type,ulong addr,ulong size);
Note that hardware breakpoints are not supported by Windows 95 and Windows 98. To assure that you can use functions listed below, call Plugingetvalue(VAL_HARDBP):
int Sethardwarebreakpoint(ulong addr,int size,int type);
int Hardbreakpoints(int closeondelete);
int Deletehardwarebreakpoint(int index);
int Deletehardwarebreakbyaddr(ulong addr);