Whatever you plug your line or guitar into is going to determine how good it sounds. Simply plugging into the integrated line in on your motherboard is going to sound pretty horrible.
If this is a permanent solution, I would recommend getting a pro-audio level PCI card or USB setup. Like a Digi-design mbox: Mbox 2 Family
There are cheaper solutions too, but I am use to using Pro tools, so that is my recommendation. You can get all sorts of plugins for amps that will actually sound pretty **** good. Not 100% like the real thing, but a good recreation.