Winning Iowa would be significant, but it's not determinative of who will win the nomination. Huck won in 08 and never got off the ground. McCain was fourth. Here is the recent history:
2008 - Mike Huckabee (34%), Mitt Romney (25%), Fred Thompson (13%), John McCain (13%), Ron Paul (10%), Rudy Giuliani (4%), and Duncan Hunter (1%)
2004 - George W. Bush (unopposed)
2000 - George W. Bush (41%)[citation needed], Steve Forbes (30%)[citation needed], Alan Keyes (14%), Gary Bauer (9%), John McCain (5%), and Orrin Hatch (1%)
1996 - Bob Dole (26%), Pat Buchanan (23%), Lamar Alexander (18%), Steve Forbes (10%), Phil Gramm (9%), Alan Keyes (7%), Richard Lugar (4%), and Morry Taylor (1%)
1992 - George H. W. Bush (unopposed)
1988 - Bob Dole (37%), Pat Robertson (25%), George H. W. Bush (19%), Jack Kemp (11%), and Pierre DuPont (7%)
1984 - Ronald Reagan (unopposed)
1980 - George H. W. Bush (32%), Ronald Reagan (30%), Howard Baker (15%), John Connally (9%), Phil Crane (7%), John B. Anderson (4%), and Bob Dole (2%)
1976 - Gerald Ford and Ronald Reagan
http://en.wikipedia.org/wiki/Iowa_caucuses#Republicans
That's a 4-3 edge "for".
However, if we also add in the Democrats.
January 3, 2008 - Barack Obama (38%), John Edwards (30%), Hillary Clinton (29%), Bill Richardson (2%), Joe Biden (1%)[15]
January 19, 2004 - John Kerry (38%), John Edwards (32%), Howard Dean (18%), Dick Gephardt (11%), and Dennis Kucinich (1%)
January 24, 2000 - Al Gore (63%) and Bill Bradley (37%)
February 12, 1996 - Bill Clinton (unopposed)
February 10, 1992 - Tom Harkin (76%), "Uncommitted" (12%), Paul Tsongas (4%), Bill Clinton (3%), Bob Kerrey (2%), and Jerry Brown (2%)
February 8, 1988 - Dick Gephardt (31%), Paul Simon (27%), Michael Dukakis (22%), and Bruce Babbitt (6%)
February 20, 1984 - Walter Mondale (49%), Gary Hart (17%), George McGovern (10%), Alan Cranston (7%), John Glenn (4%), Reubin Askew (3%), and Jesse Jackson (2%)
January 21, 1980 - Jimmy Carter (59%) and Ted Kennedy (31%)
January 19, 1976 - "Uncommitted" (37%), Jimmy Carter (28%) Birch Bayh (13%), Fred R. Harris (10%), Morris Udall (6%), Sargent Shriver (3%), and Henry M. Jackson (1%)
The number goes up to some like 12-5