You need to edit the boot.ini file.
See the section on removing an OS and setting the default OS.
This MS KB article explains all:
  http://support.microsoft.com/default.aspx?scid=kb;en-us;289022



Jim Stewart wrote:
> Recently I installed a 300gb SATA HD in my Intel 850 MB system, and installed a fresh copy of MS XP SP2 on it.. I had left the original 60GB boot drive C in place. Now I must have the 60GB drive in place, and cannot have a third rive installed because the boot sequence, which gives a choice of 4 OS to boot from, is on it. How can I haave the 300gb drive be the only drive and boot from it? (of course I could reinstall the OS I know).
>
> Jim
>
>          PCBUILD maintains hundreds of useful files for download
>                      visit our download web page at:
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>
>

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