While Henin stormed into the final with a crushing 6-2 6-3 win over Russian Anna Chakvetadze, Williams needed almost two hours to tame gritty Israeli Shahar Peer 7-6 (7-4) 6-1.
Henin and Williams have met eight times in their careers but Saturday's clash will be the first since the muscular American won a semi-final meeting with the Belgian at Wimbledon nearly four years ago.
Williams leads the series 5-3 with all three of Henin's victories coming on clay.
"It's a long time that we didn't play each other," Henin told reporters. "She looks like she's healthy now and very focused on tennis.
"I really wasn't surprised the way she came back in Australia. When she's healthy and really focused she's a great champion.
"We had a couple of good fights in the past.
"I know she has a lot of motivation but I also have a lot of motivation and the best will win."
CONTRASTING STYLES
Two players of contrasting styles and physiques, Williams and Henin's careers have shared a common path with their domination of the sport interrupted by injuries and personal problems.
Henin missed large parts of the 2004 and 2005 campaigns with a respiratory illness and knee injury.
She returned to the top of the rankings in 2006 with the help of a victory at the French Open but delayed her start to the current campaign following a split with husband Pierre-Yves Hardenne.
The feisty Belgian, however, has been almost unbeatable since her return, reaching her third consecutive final after collecting back-to-back titles in Dubai and Doha.
After playing just four events all last season because of a knee injury, Williams made a spectacular comeback in January lifting her eighth grand slam title at the Australian Open.
But the American was quickly back on the sidelines with yet another injury and is now playing her first event since Melbourne, advancing to the final without dropping a set.
In men's play, Croatian Ivan Ljubicic and Argentine Guillermo Canas, who shocked world number one Roger Federer with a fourth round upset, booked their spots in the semis with straight sets victories.
The men's other semi-final place will be decided on Friday when Britain's Andy Murray takes on Serbia's Novak Djokovic.
Ljubicic, who lost in last year's final to Federer, ended any thoughts of an all Argentine semi-final blasting his way past Juan Ignacio Chela 6-3 7-5 while Canas battled past Spanish sixth seed Tommy Robredo 7-6 6-1.
Back on the ATP Tour after serving a 15 month drugs suspension, Canas had eight break points in the opening set and could not convert any of them but prevailed in the tiebreak 7-5.
The Argentine then pounced on the dejected Spaniard, sweeping through the opening four games of the second set to take control of the match.
