Hurray! Didn't know how that would turn out, since prior decisions have not been too good. The Supreme Court just ruled in favor of George Lane who uses a wheelchair and sued because he had to crawl up two flights of stairs to get to a courtroom. Later, he refused to crawl again or to be carried by officers to the courtroom. He consequently was arrested and jailed for failure to appear.
The Government claimed that the ADA didn't apply to it. It argued that Title II of the ADA, which requires state and local governments to make their facilities and services accessible, was unconstitutional. It argued that Congress had overstepped its authority in passing the ADA when it came to regulating states.
Fortunately, the Supreme Court upheld the ADA. It ruled that Lane has the right to sue and seek money damages.
It would have been a deep body blow to disabled patrons of state and local libraries if it had turned out the other way - and it was a close one. 5-4 decision.
For regulations on physical access to libraries see ADAAG, especially No. 8. See also Dept. of Justice info on Accessibility of State and Local Government Websites to People with Disabilities which directly applies to state and local library websites.