the sad fact is that you're sharing your limitted bandwidth with your parrents. The more they use the internet , the less bandwidth is available for you. I have to ask, what the heck are they doing on the internet that is slowing you down so much?
You could try upgrading your cheap hub to a cheap switch. This would eliminate any bottlenecks caused by colisions on your network. But seriously, I don't think this is the prob. Your cable modem is probably not stressing your 10 megabit hub and cards. More likely you've got configuration problems. Try removing any uneeded protocols. All you really need is TCP/IP for internet access and even file and printer sharing between computers on your network.