Assuming the user has allready logged in and you have a vaild faceb0ok session, you could use something like this to get you started:
- (void) post {
postingDialog = [[[FBStreamDialog alloc] init] autorelease];
postingDialog.delegate = self;
postingDialog.userMessagePrompt = @"Prompt the User:";
NSString *name = @"Name of thing"
NSString *href = @"http://www.example.com"
NSString *caption = @"This is a caption"
NSString *description = @"This is a description";
NSString *imageSource = @"http://example.com/1.png";
NSString *imageHref = @"http://example.com/1.png";
NSString *linkTitle = @"Link title";
NSString *linkText = @"Text";
NSString *linkHref = @"http://www.example.com/iphone";
postingDialog.attachment = [NSString stringWithFormat:
@"{ \"name\":\"%@\","
"\"href\":\"%@\","
"\"caption\":\"%@\",\"description\":\"%@\","
"\"media\":[{\"type\":\"image\","
"\"src\":\"%@\","
"\"href\":\"%@\"}],"
"\"properties\":{\"%@\":{\"text\":\"%@\",\"href\":\"%@\"}}}", name, href, caption, description, imageSource, imageHref, linkTitle, linkText, linkHref];
[postingDialog show];
}