Hi Remco,
According to your post, you can customize the NewForm.aspx to add the additional feature. Please refer to this
document to customize the newform.aspx, you can add custom list form and add control to it. Develop a webpart to query the detail of field, you can query the detail information by following codes:
SPWeb web = Common.GetCurrentWeb();
SPList announcementList = web.Lists["Announcements"];
SPQuery query = new SPQuery();
query.Query = @"
<Where>
<Eq>
<FieldRef Name='Title' />
<Value Type='Text'>TitleOfItem</Value>
</Eq>
</Where>
<OrderBy>
<FieldRef Name='Created' />
</OrderBy>";
query.RowLimit = count;
SPListItemCollection announcementCollectionList = announcementList.GetItems(query);
DataTable dt = null;
dt=announcementCollectionList.GetDataTable();
You can query the detail information when a user have selected an item.
Thanks.
Lambda Zhao
TechNet Community Support
