You want to really help people out? Have Av and firewalls already installed... and not Norton or McAfee, which are useless.
AVG and Avast are both good. Try striking up a diologue with a few of the other AV companies, like Trendmicro or Computer Associates, and see if you can get a good deal for putting their software on your systems (well, giving the options).
Good spyware removers would be a good idea as well.
Install a decent selection of wallpapers for desktops. The ones that come with Windows are well worn and tired. Several nature shots, weather shots, space shots, cool graphics. Check out http://customize.org/
for a few thousand cool examples of what can be done/offered.
Tech support needs to be available and knowledgable. When something goes wrong, they need to be able to contact someone NOW, and that someone needs to know the answer NOW. Email, IM, chat, and phone are good options, as is a good website with FAQ and boilerplates for most common problems.
Make sure that you are putting out good quality. Nothing screams "incompetent" louder than to receive a computer and parts have fallen off/out of it in transit.