To install or remove programmes with ubuntu there is a programme already aboard called Ubuntu Software Centre which will lead you to a huge array of free software (including Antivirus) and install it for you.

As previous posters have said, few Linux users see any need for AV as the system is inherently less vulnerable than Microsoft's products, and the main use of AV on Linux machines is to avoid being an uninfected carrier of a virus.

Ubuntu support can help in various ways, there are also users here who know a lot more than I. As a non-techie who probably uses his machine much as your friend wishes to, I can say that Ubuntu will fulfill his needs without hassles (or AV), but updating is a good plan.