A California judge has approved Microsoft's $1.1 billion settlement of a state anti-trust class-action suit against the company.

The preliminary approval was delayed for about a month because the parties could not agree on the notices that will appear in the media, in the mail and online.

The deal means individuals and businesses who bought Microsoft's operating system or productivity software for use in California between February 18, 1995, and December 15, 2001, can get vouchers worth between $5 and $29 depending on the product bought. Claims valued up to $100 or for up to five product licenses can be made without any documentation.

The vouchers can be used to buy computer hardware or software from any vendor. Vouchers up to $650 in value may also be sold. Two-thirds of any unclaimed settlement vouchers will be donated to those Californian public schools that serve children from the poorest families.

This is the largest of five class action cases Microsoft has settled so far. In each of the cases the plaintiffs allege Microsoft overcharged for its software. Microsoft has not admitted guilt.

Lawyers representing groups of Californian consumers will advertise, send out email and regular mail, and set up a Web site so eligible software buyers can get a claim form and file claims, they said in a statement.