The just-released Statistics of Income Bulletin (Fall 2004) includes  Individual Income Tax Returns, 2002 by Michael Parisi (SOI) & Scott Hollenbeck (SOI).  Here is the summary:

Taxpayers filed 130.1 million individual income tax returns for Tax Year 2002, reporting $6.0 trillion of adjusted gross income.

For related data, see here.  For other individual income tax data, see here.