Can a lesbian have a baby boy?

Yes.. Sure. Lesbians can bear children the same as non-lesbian women.
Without a doubt. Being a lesbian has nothing to do with the sex of a child. Despite your sexual preference making a child still requires an egg (from a woman) and a sperm (from a man). The egg carries the sex chromosomes that make her female, xx; while the sperm carries those that make him a male, xy. A female donates an x and a male donates an x or y, actually determining the sex the baby will be.
Depends. Women of any sexual orientation of child-bearing age may experience pregnancy and have biologic children. Sexual orientation does not direct the biologic ability to conceive.

Related Questions

Can a lesbian can have a baby boy?

Yes. Only if she gets pregnant or adopts.
Yes. Any woman of child bearing age can have a child, assuming she is otherwise healthy. Her sexual orientation is not associated with her fertility, rather her choice of partner in her relationships.
Equal chance. A persons sexual orientation does not change the gender chances of conception. The lesbian would need a male sperm donor to become pregnant. The sex chromosome of the sperm that fertilized the egg will determine the sex of the fetus.