"the line in port on the computer"
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of the on-board sound card is
DAW recording 101: on board sound cards are useless
On board sound cards, the one that comes built into your motherboard is designed to make beeps and whistles and now-a-days telephony. It is not designed for high qualily, low latency sampling.
No matter what machine you have, you will get very poor performance with an on-board sound card.
With Windows, you'll need a sound card with ASIO drivers that was designed for studio use. It doesn't have to be mutli-channel, or even high bit/frequency sample rate. But it needs decent ASIO drivers. If you want to record good quality, you'll need something with decent AD converters that can sample high bit rates at high frequency.
DAW recording 102: get a decent machine
It's not so much that the netbook is under powered for sampling. It's that it probably has cheap/poor quality components. I'm specifically reffering to the either the lack of firewire or a cheap chipset. USB will almost never achieve low latency. The way zero-latency monitoring is done with USB devices is the sound is monitored before it enters the USB bus. This is a good solution. However, you will not be able to hear any FX. Also, any software synths or samples will become difficult to play.
The reason why you can acheive lower latency with firewire is because firewire has it's own dedicated processor and in turn also puts less load on the CPU. However, poor qulity firewire controllers have their own set of problems.
If you are only recording one instrument at a time and you don't want to play software sythns/samplers, you could do fine with a stereo USB sound card and your netbook. There are many with built-in mic pres for very cheap.
You might be able to also get some alternate drivers that may emulate zero-latency monitoring. However, this is highly unlikely simply because of the AD-bus-software-bus-DA round trip.
Windows Vista and later have considerable amount of overhead. If you want to have a well performing machine, use linux or Windows XP. Of course you could also shell out for an Apple, but if you know what you are doing, Apples offer no extra benefits.