Ahh, Metal Gear. Perfect gameplay, horrid gut-wrenching vomit inducing piece of shit story and dialogue. What a mixture of love and hate.
Yes, you crawl beneath the lasers. I think there is one point where you might shoot them but I dont remember.
www.gamefaqs.com is always the place to go for this stuff.
Also, Splinter Cell is 10 times harder than Metal Gear, so beware if you rent that...