it has been illegal for a service provider to treat a disabled person "less than favorably" because of his/her disability. This law was strengthened in October 1999, when it became obligatory for service providers to make "reasonable adjustments" to the way in which their services were provided, to take into account the difficulties experienced by people with disabilities.
On 1st October 2004 the law will be amended yet again, but this will mainly affect physical access to commercial premises.
It doesn't matter that a person doesn't pay for the service he/she uses - it must still comply with the relevant legislation, and this applies to web sites and multi-media products. In your case, text must be easy to read, and ideally there should be an option to view it in a larger font size.