key lengths

[Mike Thompson]

How is key length for a table defined?  It seems that the default is 255
bytes, but in the online docs it mentions 500 byte keys.  I happen to
have some very long case sensitive strings that I need to use as keys,
but mysql complains when I try to create a table as such

CREATE TABLE foo(
	id INT NOT NULL AUTO_INCREMENT,
	name BLOB NOT NULL,
	PRIMARY KEY(id),
	UNIQUE(name)
);

Any thoughts?
	--m