For a complete understanding of this, I'd recommend reading:
http://www.codeproject.com/KB/install/vsSetupCustomDialogs.aspx
In short, you've already added the shortcut and created a new dialog window from the "View" -> "User Interface". All that's left is setting the condition property. You can't change this property of the shortcut itself, but you can change it for "User's Desktop".
For that condition you might want: CHECKBOXA1=1 which means the item is created/activated only if the CHECKBOXA1 is checked. 0 for unchecked.
A reference to conditional syntax is here:
http://msdn.microsoft.com/en-us/library/aa368012.aspx
EDIT : I just tested this and it looks like the Visual Studio installer is pretty unintuitive. The answer I provided doesn't work. You have to go about this is an ass-backawards way. This article better describes the process than I can: How do I specify Visual Studio Installer Conditions?
Overall, the Visual Studio installer is intended for fairly vanilla installs. It can do a LOT more, but it's cumbersome to do so. You can even have custom actions run during the installation (ie: run your own executables). The Visual Studio installer is included with VS 2010, but it will be removed in favor of InstallShield LE in future version.