Creating custom workflow on shareporint 2003 on existing portal- VERY URGENT

Question

Hi Shafiq
I hope you get to answer this question for me I have not got any answer from anyone or google

1) There is an existing sharepoint portal
2) In the portal there is a list
3) In a list when you create a new item -
4) in the new item there is a n option to select an option - Yes or no
5) If you select Yes then it should mail to set of users

This requires a set of custom workflows
this is ONLY in sharepoint 2003 not in 07 or anything else

How do we deploy a custom workflow in to the existing sharepoint portal

Or how do we achhieve this
If you are able to do thsi can you please email me on [email protected]

Or can you please call mail me a solutino

Thanks
Ven