Win 7 - Apps not running but taking memory

I’m running Windows 7 Home Premium and upon startup there are no applications running.
However if I look in the task manager I see

Steam - 150,000K memory in use
uTorrent - 6,400K memory in use
Open Office - 5,400K memory in use

and on and on…

Why are these programs taking up memory on startup and can I prevent it?

These are the little “helper” apps that are a major culprit in slowing people’s PCs down after a year or so of use. If you install something and opt for the recommended settings, you will probably install this sort of mostly-useless crap alongside the thing you actually wanted to install. The Open Office startup app, for example, just makes Open Office files open more quickly. You don’t really need it unless you use Open Office regularly. Some manufacturers love to install update utilities, which check for newer software every time you boot up. And so on.
I always try to use the Custom Install option when I’m installing software, and opt out of as much as possible. I still end up with useless auto-loading crap, which I get rid of with one of the many startup configuration/clean-up utilities that are available. Msconfig is the one that comes with Windows (see the Startup tab).

That did it - thanks!