I am going to Rome in August for 10 days. Is there anywhere I should avoid? Or anywhere I should not miss?

I like museums, art galleries, history etc. I was told that one has to queue for hours to get into St. Peter's. Is that true? Should I pay a local tour guide company to take me around or should I make my own way? I know that August is very hot there and some places are closed. I will be staying in the Termini area.
Thanks in advance for any experienced advice.

There are some great independent Roma and Italy tour guides here:

http://www.viamigo.com/tours/rome.html
http://www.viamigo.com/tours/italy.html

Many of them offer a customized experience, and you can contact them to tailor the tour to the museum, art gallery, and historical sights you want to see. They should also have a good idea of the St. Peter's Cathedral scene and can fill you in on the weather and the sights that might be closed. Hope this helps!

Watch out for little street urchins who try to put pieces of cardboard on you. They are pick pockets and your wallet will be miles away before you can react.

Make reservations in advance for places like the Colosseum or Vatican museums. The long lines are for the museum; while there will be lines to get into St Peter's, I've never had particularly long waits.

With ten days, you'll have time to see some of the lesser attractions in Rome and take some side trips. I'd highly recommend considering going to Florence for a day or two and/or Capri, Pompeii, Tivoli, Orvieto, or Ostia Antica. All of them have interesting things to see and do. They're also all accessible using the train system to get around. You can use this site to check specific schedules and prices: http://www.trenitalia.com/en/index.html

It's true that a lot of us will be on vacation in August, but the major tourist attractions won't be affected. The antidote to the temperatures is lots of gelato.