You may do it alone, but a little help won't hurt. Just choose friends who are not very talkative and knows how to keep a secret. Next step is to make the invitations. The best place to find one is online. From birthday invites to baby shower invitations, it's all available in the world wide web.
Choosing the caterer, venue and the different activities for the party can be assigned to your chosen not-talkative-friends.
Planning a surprise party can be tiring but fun!