From Hotline, which tallied all the votes for Democrats and Republicans in contested House races last year:

        GOP U.S. House Votes     Dem U.S. House Votes
2000    47,238,467 (50.3%)      46,701,783 (49.7%)
2002    37,428,113 (52.5%)      33,905,437 (47.5%)
2004    56,112,869 (51.4%)      53,128,318 (48.6%)
2006    35,904,068 (45.9%)      42,291,298 (54.1%)

4-yr
Total    176,683,517 (50.1%)    176,026,836 (49.9%)