VA Linux Systems Inc., a maker of software and computers based on the free Linux operating system, agreed to buy Andover.Net Inc. for about $1.04 billion in stock and cash to get its network of Web sites for Linux programmers. Andover.Net runs Web sites that provide news, downloadable software and forums for those who use Linux and hope it will challenge the dominance of Microsoft Corp.'s Windows operating system. VA Linux will exchange 0.425 of a share of its stock for each Andover.Net share. About $60 million of the purchase price will be in cash. Andover.Net jumped $9.13 to close at $45.13, while VA Linux fell $8.88 to close at $128, both on Nasdaq.