IRS has published an updated version of IRS Publication 1220, which covers electronic filing of 1099s for tax year 2008. [IRS PDF Download site]  As result of the new rules for 2008, the IRS will no longer accept magnetic media, which makes Form 4804, Transmittal of Information Returns Reported Magnetically, obsolete.

If you are new to filing information returns, wikipedia has a some good information on 1099 filing.