Hooover is right about HHC by emunutz being an amazing way to customize your HTC Home plug-in. But that's the plugin which usually is displayed right above the plugin with the 5 icons Racincason's original post asked about. The OP plugin is (was) called QuickLauncher in WM v6.0, but if you're running WM v6.1 its name got changed to OperatorLauncherPlu... Verify this by tapping:
Start > Settings > Personal (default tab) > Today Screen > Items (tab)
To change icons used by this plugin involves XML coding hacks. Good info re this approach is in the PPC Geeks link provided above by eye.ofthe cyclone, but there are more user friendly alternatives. Info re this approach is also available on PPC Geeks, starting here:
http://forum.ppcgeeks.com/showthread.php?t=37770
Hope this helps, MrG