I'd also guess that svchost.exe is likely to be involved, with either the dreaded Windows updates behind the problem or possibly your antivirus program. (Microsoft Security Essentials and Windows Defender are notorious for causing such problems. Norton used to be bad, got better but now has a poor reputation again for hogging resources. Kaspersky used to be good but is now also prone to similar problems. I gave up on AVG after I found that it had started to hog resources too ).
The problem with trying to make sense of what's shown in Task Manager is that programs such as Firefox (just as an example) tend to go into overdrive (apparently using a lot of resources) when there's actually something else going on in the background that's stopping Firefox (or whatever) from doing its job normally.
I've also got a Windows 7 netbook, which I use regularly. After loads of problems like yours, I've got it to function reasonably well by
(a) turning off Windows updates ;
(b) using Avast as my antivirus program ; and
(c) gaining additional RAM by using Ready Boost:
http://www.dummies.com/computers/operating-systems/windows-7/how-to-use-readyboost-to-speed-up-windows-7/
As well as those suggestions, I'd also recommend a scan with Malwarebytes (or AdwCleaner), as malware can sometimes be the cause of such problems.