I plan to go to Russia next May and many of my friend have warned me about how danger it is to backpack travel in Russia especially for women. I'm thinking about hiring local guide or joining group tour when in Moscow and Peterburg. Anyone can suggest me where can I hire local guide/join group tour and what 's the price range?

Generally speaking Russia is not dangerous for women, that said, from your name I assume that you are from Thailand and people from East Asia do get hassled more than westerns.
Instead of taking a group tour, I would suggest staying at hostels so that you can meet people with whom to travel, taking walking tours with a company like Patriarshy Dom in Moscow or Peter's Walking tours in Petersburg. Supplement these with bus tours if you want. Both companies can make suggestions. In reading through the Patriarshy Dom tours, note that they make up the schedules about 6 weeks in advance so if there is a tour you would like and you know your travel dates, then write them and ask if they can schedule it when you will be in town. They are generally very accommodating in this way.
I am sure that you know that Thais are among the very few who can enter Russia as tourists visa free.
If you have more questions, let me know.
Ruth

Thanks. I know that Thais do not need visa to enter Russia but not sure how long this will last. Also heard that some Thais had problem entering Russia as Russian officials at customs do not generally know about this new rule. In anticipating this potential problem, how should I prepare for this? In which website can I get this document that have details on this rule and period of its implementation?
Go to the Russian embassy in Bangkok and get them to give you something that explains the Visa-waiving Agreement (Ordinary Passports) which was signed by Russia and Thailand in 2005. The website lists the name but it doesn't appear to have a copy of the agreement. Another possibility is that there might be information on the Thai Ministry of Foreign Afairs website.
I don't think that it will change because Russians want to come here to Thailand.
Ruth