Try to sell your dad on a spending rate. You can't guarantee a computer to last 15 years, but if you can figure out his risk tolerance and try to maintain his spending allowance. If he bought two 486s in 1994 and each were $2000 and the value of the dollar being about 1.3 what it is now, so he spent $5200 in today's currency back in 1994, that's about $350/year. Do you think with these numbers, you could convince him that it would be worth buying two netbooks for about $350 each, with the high chance they would last two years? If they last an unheard of 3 years, he would actually be spending less per year 700/3 ~ 250. If they last more he will actually be saving money over his old setup.
In fact, if he took the same amount of money, $5200. Invested $700 in hardware. Put the remaining 4500 into bonds at 5%, over 15 years he could almost buy a new netbook every year on interest alone.