I would like to know how can we build a custom field control in sharepoint. Following is the scenario i am looking into it:

1. Textbox control with browse button

2. When we click on browse button, need to display a popup (like business data dialog box) where i can search for project id from oracle datasource and then select the project id(s) from the search results. Selected project id(s) must be concatenated with colon or semi colon and display back to original text box.

I guess requirement is very clear. Please help me how to do this type of things in sharepoint. I have never done these type of requests earilier. Thank you very much for you help.