You could try Bandicam, it's a decent alternative to fraps, and instead of the stingy 30 second limit you get 10 minutes for each video. If that's not enough then you might have to resort to free Screen Recorder programs which shouldn't have a time limit but usually have the most impact on performance.
thanks a lot, actually did tried got during the google search phase..
right now the best i ever tried is ezvideo.com
it can't record the audio directly but probably able to if my pc got a mic.
here's my test record
the max output resolution is 720p for my 1920x1280 display but quality is decent enough
ps FYI, i just found that it's impossible to do screen record in full screen mode, all you get is a black screen. thanks to ezvideo's hint i switch to window mode and get it done.
probably need to re try some of the software i tried earlier which i thought fail to record...