I'm looking at the possibility of having to buy a new MB. But I'm kind
of new to building them. I've only built 1 so far and I don't have the
money to go screwing this up nor the patience of getting it wrong and
having to send it back for an exchange, if that's allowed.

I have an ATX full size tower. Will a microATX MB fit in it without any
trouble?

Could anyone reply with what I should be careful about, or specific
boards to stay away from? I'm on a very very tight budget so I'll be
shopping in the <$100.00 range with either tigerdirect or newegg...