11.04

(and works for all versions since 11.04)

The use of alacarte in the current version of xubuntu is perhaps not a good choice because of its perceived gnome dependencies - it is actually packaged wrongly, but that's a different story.

Xubuntu / Lubuntu Menu editor

You could try the following java based menu editor which works for both Xubuntu and Lubuntu:Image may be NSFW.
Clik here to view.

To install, download and extract into your Downloads folder

Then open your terminal:

if you havent already installed java

sudo apt-get install openjdk-6-jre

followed by

cd ~/Downloads/lxmedchmod +x install.sh

If the folder /opt does not exist then

sudo mkdir /opt

Finally

sudo ./install.sh

You launch the menu editor by Start - Settings - Main Menu Editor