Yes, more likely the two do a horrible pornography video rather then fight. But I could see a plot where they fight..
For one, Lara Croft doesn't take kindly to Duke Nukem treating her like a peice of meat.
Secondly, both Lara and Duke Nukem are in search for the same cosmic item. (Perhaps the cosmic cube?) Where Lara will swim, tumble, climb, and decipher hiroglyphics to find it, Duke will simply shoot anything with two or more legs and grunt alot hoping someone will turn it up. One alien tells both that it's inside one of thier bodies because they knew they could hide it there and no-one would find it. Lara gets it out of the alien by diplomacy and the alien learns to sympathize for infirior beings, Duke threatens to kick his ass and chew bubblegum, and he's all out of gum..
The two square off, Duke uses alien technology he finds along the way, and alot of top secret weapons even the CIA scratches thier head at, but Croft has martial arts to help her avoid ceartain defeat, and has the best tools money can buy. But despite her skill and her money, we have seen in-game she can easily be killed by a gang of thugs or a grizzly bear. Nukem's massive amount of testerone is too much for Croft to handle. And he brings her dead corpse to the secret goverment base to extract the cosmic cube. (We won't ask how the semen got in there..) and come to find out, there is no cosmic cube in there and it had to be in Duke Nukem. The aliens were smart and new to put it in the ape-man who would not only kill the only other decent threat, but be idiotic enough to walk around till time was up. Duke Nukem says "Oh sh--" and is cut off by a massive implosion of the universe. The alien terrorists win. And Duke Nukem 64's music plays as it all rolls the credits..