A simple bootstrap
                                                                    -----2004.11.1 (C) Gr1x
To make a long story short,and enough material can be found about the PC's POST procedure, I'll just show my code and explain sth important steps,I think my source code is self-explaining enough 'cause it's short and easy to understand . I have tested it with a floppy disk,  it's risky to test it with ur harddrive. If  u did do it,I  am not responsible for any damage u made : )
Environment :(Window Platform)
     a.VMWare(Optional).If u don't want to reboot ur system many times,u should get this.
     b: Nasm.(Essential). As u need it to compile ur code . u may use Ndisasm as well to disassemble the plain binary code compiled.
    c:Visual C++ 6 or Visual Stdio .Net. As we have to write a EXE to write the bootstrap to floppy.
       U may use WinHex to write bootstrap to floppy too instead of this writing a programme.
1>Write the bootstrap procedure
----------------------------bootstrap.asm-------------------------------------------------
;***************************************************
;                     bootstrap.asm: 2004-11-1 (C) Gr1x
;                     Email:gr1x@sina.com
;****************************************************
[ORG 0]
     jmp 07C0h:start                ; remember that BIOS loads this procedure in  0:7C00h,but don't count on registers like DS
                                             ;was initialized to 0. So we jump to it ourself.
    msg db 'Hello Gr1x!',0x0
start:
    ; Update the segment registers
     mov ax,cs
     mov ds,ax
     mov es,ax
     mov si,msg ; Print msg
print:
     lodsb ; loads charater at 0x7C0h:msg
     mov ah,0eh ; 
     int 10h
     cmp al,0 ;
     jne print ; 
     jmp $
     times 510-($-$$) db 0
     dw 0000h        ;or dw 0AA55h,u can write anything here,it seems that BIOS doesn't check this 2 bytes when 
                            ; it try to boot from a floppy disk
-----------------------------------------------------------------------------------------------------
OK,now compile it:
        >nasm bootstrap.asm -o bootstrap.bin
2.Now,copy this bootstrap to floppy's boot sector. If u do it with WinHex,u can omit following.
   I wrote a program which do this action.
------------------------------write_fd.cpp----------------------------------------------
//*********************************************
//              write_fd.cpp: 2004-11-1 (C) Gr1x
//               Email:gr1x@sian.com
//***********************************************

#include <windows.h>
#include <winioctl.h>
#include <stdio.h>
#pragma comment(linker,"/subsystem:console" )
void Banner()
{
 printf("---------------------------------------------/n");
 printf("  write_fd:write a file to floppy in raw mode/n");
 printf("  author:gr1x              email:gr1x@sian.com/n");
 printf("  usage:write_fd filename/n");
 printf("---------------------------------------------/n);
}

int main(int argc,char **argv)
{
 HANDLE                  hDevice=NULL,hFile=NULL;
 TCHAR                   szDevicename[64];
 LPTSTR                  szBuff=NULL;
 DISK_GEOMETRY           Geometry;
 BOOL                    bRet;
 DWORD                   bytes,bread,count;
 Banner();
 if(argc!=2)
 {
  printf("Usage:%s filename/n",*argv);
  exit(0);
 }
 __try
 {
  hFile=CreateFile(argv[1],GENERIC_READ,FILE_SHARE_READ,NULL,OPEN_EXISTING,NULL);
  if (hDevice == INVALID_HANDLE_VALUE)
  {
   printf("Error in open file %s!/n",argv[1]);
   __leave;
  }
  wsprintf(szDevicename,"////.//a:");
  hDevice = CreateFile( szDevicename,
   GENERIC_READ|GENERIC_WRITE,
   FILE_SHARE_READ|FILE_SHARE_WRITE,
   NULL,
   OPEN_EXISTING,
   0,
   NULL
   );

  if (hDevice == INVALID_HANDLE_VALUE)
  {
   printf("Error in open floppy device!");
   __leave;
  }

  DeviceIoControl(hDevice,FSCTL_LOCK_VOLUME,&count,NULL);   DeviceIoControl(hDevice,IOCTL_DISK_GET_DRIVE_GEOMETRY,&Geometry,sizeof(DISK_GEOMETRY),NULL);   szBuff = (LPSTR)HeapAlloc(GetProcessHeap(),HEAP_ZERO_MEMORY,Geometry.BytesPerSector*2);   if ( szBuff == NULL)  {   printf("Error in HeapAlloc!");   __leave;  }   bytes = 512*2;   bRet = ReadFile(hFile,szBuff,bytes,&bread,NULL);   if (bRet==FALSE || bread<512)  {   printf("Error in read file!");   __leave;  }   printf("%d bytes read from %s/n",argv[1]);  bRet=WriteFile(hDevice,NULL);  if (bRet==FALSE || bread<512)  {   printf("Error in write file to floppy!");   __leave;  }   if(!DeviceIoControl(hDevice,FSCTL_UNLOCK_VOLUME,NULL))   printf("DeviceIoControl(hDevice,NULL) error!/n");  DeviceIoControl(hDevice,NULL);   printf("Write finished!/nBoot sector in HEX:/n");  for(int j=0,int i=0; i<512; i++)  {   unsigned char ch=(unsigned char) szBuff[i];   if (j==8) printf(" -");   if (j==16)   {    printf("/n");    j=0;   }   j++;   if (ch<0x10) printf(" %2x",ch);   else printf(" %2x",ch);  }  printf("/n"); } __finally {  if(szBuff!=NULL)   HeapFree(GetProcessHeap(),HEAP_NO_SERIALIZE,szBuff);  if(hDevice!=NULL)   CloseHandle(hDevice);  if(hFile!=NULL)   CloseHandle(hFile); } return 0;}--------------------------------------------------------------------------------------------Don't ask me how to compile this cpp file!3>Type following commad in CMD    >write_fd bootstrap.bin4>OK,boot ur system with the floppy.God bless u!