If you are including the price of the OS, and the OS is Widows XP or Vista, and it is a legally purchased copy, then you need to bump the choices up even higher.
Also, I have found that most people will fall back on you for advice or help, especially if they are inexperienced operators.
It wouldnt hurt to charge a few more bucks to cover that, unless you tell them right up front that any calls will be charged for. You dont want to hurt your customers feelings when they think it just aint doing right, by charging them a service call fee, unless they agree to this up front.
Hurt feelings have a way of expressing negatives to possible word-of-mouth customers.
Especially when you have to factor in gas, wear and tear on your vehicle, Indemnity Insurance. Gee Whats that?

If you screw something up you can get sued, nice to get covered for life's little unexpected problems. Sure he is your firend, and probably still will be after he takes you to court if you break anything valuable.
I had excellent cover from my home insurance provider. Real cheap, half a million dollar coverage, should be enough.
Software licenses can be got cheaper via OEM, not retail boxed. If you are putting XP on all future PCs - look at getting bulk licenses direct from a Micro$oft preferred supplier or an outfit like Misco.
I bet TMI is at the fore front of your thoughts right now HarumaN.
But to put it in the words of your favorite character:
"If you are good at doing something, don't do it for free".