Year 10s can do the current IAA’s, they just need to bank them this summer (2008).
If your centre is not planning on making any Y10 entries until Summer 2009, then you can not do the current IAAs but will need to wait until April when the new ones will be out.
With regards to the fees example quoted above, you should bank units 1, 2 and 3 in summer 2008, for which you will be charged two entry fees (unit 1 being free), and then enter unit 4 for summer 2009 for which you would be the normal unit entry fee rate, provided it's on time.
Futher guidance on submission of Edexcel devised assessments including dates can be found on the 360Science microsite in the news section, or by clicking here.