Multiple selection in the Search Help

Hi Experts,

I am new to the CRM 2007, i implemented a Custom search help in the attribute of a context node. The search help is working fine, but in the R/3 level i can select multiple items from the search help. But in the WebUI the check box for the multiple selection is disappearing and also it is allowing me to select only one value.

Now i need to construct a search help to allow multiple values from the user .