I've started an online magazine purely as a hobby.  To date, I've been
bartering "advertising" with contacts to help promote my site.  Just
recently, I've begun to get offers from my contacts to actually pay
for advertising.  So far, I've only earned $50, but now have the
opportunity for a promotion that will bring in $1,000. I'm thrilled
about actually bringing in some money for something that's a hobby and
doesn't have a business plan, but I don't want to get in trouble for
not reporting/paying all the proper taxes.

Do I need to get a business license?  Where can I find information on
getting one?

Oh, and in case it matters, I'm located in Virginia