We'll wait for you at the meeting point at 4.30 рm on the date you reserved!
Google maps link is here.
The Alexander Column in the center of Palace Square

DETAILED DIRECTIONS FOR YOUR COMFORT:
1. Get to Admiralteyskaya metro station (Purple Line).

2. Go to Palace Square (cross Nevsky Prospect — the main avenue).

3. Find the Alexander Column in the center of Palace Square (see how it looks: http://upload.wikimedia.org/wikipedia/commons/d/d5/WinterPalaceAndAC.jpg).

Your tour guide will be near this monument with the 'Free Tour'sign. Please choose the side of the column which faces the Winter Palace (it's green).