14 years ago
The diet suggested above is fine. Just eat 5 or 6 smallish meals per day, get plenty of protein and enough carbs and fat, and make sure you eat enough calories to gain weight.
Most weight gain pills won't work - there's a *lot* of snake oil. Steroids can work, but the risks involved means I'd advise avoiding them - especially if you're just starting lifting. Creatine can be of some help, but isn't cheap and carries a risk of kidney damage.
Anyway, good luck with the lifting :)