Does anyone know the best/cheapest way for me to book a train ticket from St Petersburg to Helsinki for July? Thanks. malcolm
The cheapest thing to do is to take the bus and you don't need reservations.
If you want to take the train 45 days before departure you can buy the ticket from Petersburg to Helsinki directly from the Russian trains on the rzd.ru website. You must register first to use the ticket buying feature. Try using google.com or translate.ru to translate the pages.
Ruth

Note that there are daily busses and even taxis between StPete and Helsinki. A bus seat would be EUR 10-12-15, a door-to-door cab ride would be EUR30 (EUR35 to Helsinki airport). Both are cheaper than the train and you don't have to reserve anything in advance (well, you do for the cab - just give them a call the day before).
If you still want to go by train, have a Russian travel agent book it - or, if you're anywhere where Deutche Bahn is present, book it through them. Train 33 is Russian, train 35 is Finnish - you can probably book the latter through Finnish Railways as well. www.rzd.ru still has a way to go before it becomes user-friendly or easy to book at.