There is a thread on the Guerrillagardening.org forums, http://guerrillagardening.org/community/index.php?topic=3298.0
and a facebook group http://www.facebook.com/event.php?eid=114409348583887
for the event. Sign up for either of those to keep up to date with the plans, or keep an eye open for news at http://www.sheffieldsunflowers.org.uk
What you will need:
A bottle of water.
Something to make holes with (pencil, screwdriver, trowel, or in my case, a crutch!).
What to do:
Dig a small hole about 2cm deep, drop in a seed. Cover with soil. Water.
That's it! As many times as you like, in as many places as you feel will be cheered up by a glorious sunflower in a couple of months.
PLAN: If you want to meet up to plant the sunflowers, we will be meeting at 12 midday outside the Blue Moon cafe in Sheffield city centre, by the Cathedral ( http://www.tinyurl.com/368fz2c ). Please be prompt!
Alternatively, you can plant some seeds wherever you are in your locality.
There is also now a flickr group for this event: http://www.flickr.com/groups/1367558@N25/