SharePoint 2010 Autocomplete Lookup field allows type ahead functionality while looking up values from the lookup list. It uses REST for specifying filters.
stsadm.exe -o addsolution -filename C:\NY.Autocomplete.LookupField.wsp
stsadm.exe -o deploysolution -name NY.Autocomplete.LookupField.wsp -immediate -allowgacdeployment
Consider a list named Company with following fields:
Title: consisting of names of companies
Create a custom list named Employee and add create a column of type Autocomplete Lookup Field in it as shown:
In the REST Filter specify the following filter: and Active eq true
This will make sure that only those companies show up which have Active set to Yes.
Following image shows the results while using the Autocomplete Lookup column
For more information please visit http://sharepointnadeem.blogspot.in/2012/03/sharepoint-2010-autocomplete-lookup.html