Programs on the Taskbar are usually Quick Launch programs. Right click on the icons you don't want and select DELETE. Then run MSCONFIG, then go to the Startup tab and uncheck those (the same ones) you don't want. That should prevent them from reloading.
http://windows.microsoft.com/en-US/windows-vista/Add-or-remove-programs-on-the-Quick-Launch-toolbar
Programs LOADING in the taskbar have nothing to do with Quick Launch. Quick launch is a menu of shortcuts, nothing more, so yes they are icons that show on the taskbar, but they are not running programs. Yes, this menu resides on the taskbar, but deleting things from the quick launch (if you even have that visible) will not prevent anything from loading into the system tray at startup.
The System Tray is now called the Notification Area. That is where background apps show as loaded - those are not what I call user programs in the Taskbar. That area basically belongs to Windows.
The Q/L area on the left side are user designated shortcuts. The icons on the far right are system notifications. Typical icons are speaker control, Internet access, Network Access, Roboform, AV running, safe remove, etc. And system clock.
Between the Q/L are and the Notification area is what I see as the Taskbar, and usually only open/running programs have an icon there. If OP is referring to the Notification Area, a.k.a. Tray, then MSCONFIG is the normal on/off tool unless you want to get involved with Registry editing.