As Zara Philips and Mike Tindall get ready to say "I do" this weekend in Edinburgh, dozens of friends and family -- including the Duke and Duchess of Cambridge, in a stunning green dress and black heels-- were on board the Royal Yacht Britannia on Friday for the start of the festivities.

Prince William's cousin -- and Queen Elizabeth's first granddaughter -- is marrying rugby star Tindall in a ceremony that begins at 3 p.m. on Saturday.

According to the Daily Mail, the church, which is under heavy police guard, has been decked out with more than 400 white roses and hundreds of beech tree branches. Florists have also brought dozens of white carnations and white stargazer lillies into the chapel, along with small box trees and ivy.

Phillips is expected to wear a wedding dress by designer Stewart Parvin, something her reps won't confirm. Similarly, there is no word on who will be in the bridal party.

On Friday night -- which happens to be the 30th anniversary of the day William's parents, Lady Diana Spencer and Prince Charles -- married guests will gather at a pre-wedding celebration.

People magazine reports that younger guests are expected to party on the Windsors' retired vessel, the Royal Yacht Britannia, which is now moored in Leith docks.

The wedding of Phillips, 30, and Tindall, 32 -- whose engagement was announced in December -- will mark the first time William and Kate have been seen together since their tour of Canada and Los Angeles earlier this month.

While in Edinburgh, the Duke and Duchess of Cambridge will be called by their titles in Scotland, the Earl and Countess of Strathearn.