Hi jellybean
I can't stress enough the need for the figures to be right from the start or the iva will surely fail which will not help you.
I would make a list of income and expenditure by yourself and what you need to be able to live and not worry too much about what you can have. IVA's are individual and your expenditure may differ a lot from someone else's.
The below link will take you to a post from last year which lists the cccs guidelines which creditors seem to think reasonable.
http://www.iva.co.uk/forum/topic.asp?TOPIC_ID=7238
Don't worry if any of your figures are more, and if you have reasons for higher figures explain them. I for example have an oil central heating system and oil prices are very high.
Sit down with all your utility bills, food reciepts and anything you can think of (prescriptions for medicines, glasses, contact lenses, dentist, etc) and list your income and expenditure and then discuss with your IP.
My i&e was never dictated to me and I think this is dangerous
Good luck
Emma
Be positive & look after yourself, there are more important things in life than debts....
Best Wishes
Emma x