How do you search multiple forums?

[Wongod]

I want to set up a form that when a user types in a value, it will search for it in 2 or more forums. Right now the code I have for searching for 1 forum is:

<form action="forum/search.php" method="post" name="search1">
							<input type="hidden" name="do" value="process" />
							<input type="hidden" name="showposts" value="0" />
							<input type="hidden" name="quicksearch" value="1" />
							<input type="hidden" name="s" value="" />
							<input type="hidden" name="forumchoice[]" value="2" />
							<h1>Search:</h1>
									<input type="text" size="15" name="query">
									<a href="#" onclick="document.search1.submit(); return false;"><img border="0" src="images/icon_arrow_blue.gif" width="13" height="13"></a>	
		</form>

How can I change this to add another forum?