Do we need to register for self assessment?

Hello,

I am part of a very small group of people organising a collectors convention with all proceeds going to charity.

We have set up a bank account in the name of the organisation and have a committee structure.

2007 will be our 4th year and each year we raise more and more money for a different charity. Last year we raised over £1000 after expenses.

We are considering holding back a sum (£200) each year to help us secure the next venue.

Do we need to be registered for tax with the Inland Revenue? (HM customs are they now?)

Thank you,
Freya