It's not preventable. RuneScape and Hypercam both use large amounts of processor power. Hypercam is constantly writing to the hard drive, too, and so is RuneScape, which is also constantly streaming data from the web.
The only thing you can do is try to find a screen recorder that doesn't use so much power. Generally, though, they all use a lot. RuneScape is rendering complex graphics with your CPU, and any screen recorder is having to encode a video on the fly. Two heavy processes.
Basically, there's nothing you can really do. Save possibly getting a quad-core processor and a SCSI 10kRPM hard drive.
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