I would suggest before you do anything, go here, this Black Viper's one of the sharpest guys out there:
http://www.blackviper.com/Articles/OS/OSguides.htm
Find your OS on his list, and look carefully at what he tells you about the services it wants to run, and whether you can safely disable them, or whether you can set them for manual start rather than autostart. Windows likes to start up a lot of stuff that most of us don't need.
Then run Windows Task Manager and look at what it tells you is running under the Processes tab. Where Task Manager is depends partly on how your system's been configured. It'll show up after Ctl-Alt-Del on a button in the Windows Security panel if you're system's set up with the classic interface, or it'll be available in the popup list you get after a right click on an empty part of the task bar. Any process you see running there that isn't on Black Viper's list is something one of your programs has added. If you have a Logitech mouse, for instance, you'll probably see a process called EM_EXEC.EXE running. That's the mouse driver; the system will work if you kill it off, but you won't have full functionality with the mouse. You may also see similar driver processes related to your particular hardware, like video card drivers, printer drivers, you'll see something from Nero Burning ROM if you have that, you'll see anti-virus processes (or you certainly *should*) and so on. You need to know what things are before you remove them, and you can't remove them with Task Manager, all you can do is kill them off temporarily. For that you need to get into the registry, or they'll just show up again the next time you reboot.
Unless you're a serious expert, I wouldn't recommend doing that manually with regedit. And if you know how to do that, you don't need any help from me anyway. There are multiple places in the registry that things are started from, and there are freeware utilities that'll guide you through it. I use one called StartupCPL, which you can find at
http://www.mlin.net/StartupCPL.shtml. Its greatest advantage to me is that it shows the full path name associated with the processes Windows starts, which'll give you a clue about whether you can safely remove something. Note, though, that what StartupCPL tells you gets started isn't necessarily what the Task Manager will show you is running. It doesn't, for instance, tell me that EM_EXEC.EXE is started anywhere, nor is there any indication that it gets started when I do a manual search in the registry for Run keys. What I see in the registry getting started is a process called Logi_mwX.Exe, but it doesn't show up in Task Manager's list. What I presume is happening is that the Logi_mwX process starts up other processes then disappears, leaving them running.
Be careful though. It's altogether typical of Microsoft to make the core of the system a large and easily corrupted database and provide no good maintenance or management tools for it. With regedit, for instance, search the registry for the name of an application you've uninstalled. Odds are you'll find it's left footprints all over the registry. That'll happen every time you install or uninstall things, the database doesn't get properly cleaned out, over time it just gets bigger and bigger and becomes an increasingly inaccurate description of your system. No registry cleaner (I use
this one and
this one) can fix that, they can only postpone it. At some point, though fortunately it usually takes a few years, you have to wipe the drives and start over to get a clean system.
