You can download avast Home or Pro version, the trial gives 60 days unrestricted use, when it is installed you/they can use the Demo key.
If they qualify for Home use they can later register on-line and get the free registration key sent to them. avast! 4 Home Registration
You can also periodically download the latest VPS so you have a recent VPS without having to go on-line and risk further infection. avast! VPS Update - Manual Download
With both the program setup file and the latest VPS file on the thumb key your set to install avast on their infected machine.
I have created a folder on my HDD called CDTemp\UsefulApps, where I keep a range of useful apps, just for the purpose you mention. I keep that reasonably up to date and when going to help someone, I just burn a CD and take that with me and leave them with a copy.
And David, I just wanted to add one more very useful utility, especially for all those which don’t know how to protect their kids from surfing and visiting those ugly web sites… This useful software is called NAOMI and it’s made by Radiant. Wonderful person by the way !
This is short explanation what it actually does (from their web site):
Naomi is an advanced internet filtering program, easy to use and totally FREE, intended for families and parents in particular.
Naomi is able to constantly monitor all internet connections, protecting children from inappropriate online material - such as obscene or violent contents; pornography and erotism in the form of images or texts; sites that popularize drugs; gambling games; terrorism; hate propaganda; occultism; sects; blasphemy, etc.
The filtering technology employed in Naomi 2.5 features:
Heuristic analysis capable of recognizing new material automatically.
Semantic analysis of web pages contents and analysis of their addresses and links.
Recognizes the major languages.
Recognizes ICRA labelling system.
Monitoring is not limited to web sites, but covers the whole local internet traffic.
Works with any software application, and does not alter their settings.
Password-protected (the password is chosen during the installation).
Does not require configuration.
Can be used on slow connections (it does not perform any download in background).
More can be found in this thread started by our friend Fast:
Also, important to mention… program is freeware, but donations are welcome. Please note that should you decide to donate, you are kindly asked to do so, but NOT to the author of the program, but to Compassion, an organization devoted to helping children in need in many countries.