For a laptop to handle streaming audio for sample libraries, in addition to handling tracks, audio, and plugins, in addition to the processor you really need the ability to have a 2nd hard drive, and if you can get 16 GB or more ram that helps.
Many laptops do not have internal capacity for a 2nd hard drive, and that can create a bottleneck, as it is potentially being asked to read and write from two locations, and deal with a whole bunch of data coming through at the same time.
You certainly would be able to do some level of projects on a laptop with a single drive, but once you start streaming sample files in addition to reading/writing audio data, I think you would run into some issues that would be beyond what such a laptop could handle.
For the money though, I would think that laptop would be OK - good for general use, and good to a point for Sonar - the battery pack is likely toast, so you also face either replacing that (and I would replace the hard drive too), OR losing data and possibly corrupting files when the system instantly were to shut off if the power adapter to the laptop was jarred or came loose.
Bob Bone