Without exact names, locations and dates no archive is going to help you. Postings on various on-line billboards remain a possibility, but the Russian net is still in a nascent state, and the number of people with the WWW access is too small to hope that such ads produce tangible results. Nevertheless, I know of several cases of BBS announcements that have actually ended in finding ancestors. The key factor of success was either a very rare surname or one belonging to a famous family. If you have the basic data ready, the best way for a foreigner would be to retain a reliable contact in Russia.
All correspondence is done in Russian.
Several local phone calls may be also helpful. Russian archives, as well as other government offices here, tend to charge foreigners ten-fold or more the fees they charge Russian citizens. Payment is made in Russian rubles only, by mail transfers or bank transfers to the archive's banking account. It is impossible to do that from abroad. This arrangement greatly facilitates matters.