Ekg+Arduino+Vdip

I''ve built a portable analogic EKG some days ago.I checked my signal with an oscilloscope and it works fine.The project was built to make a connection with arduino duemilanove ATmega168,which convert analog signal in digital signal and to write it in numeric format with VDIP module in a memory stick.Well,I need to write fast from Vdip to stick(I think min.400 samples/sec) in order to get an accurate graph.I will put my numbers in *.txt file and after that I will get the graph with a program such Excel.My problem is that I'm not so good at software and I don't know if I can write so fast from Vdip to usb. If somebofy can help me with some advices or soft,I will be very thankful!

How much data is there? Maybe you should consider using a buffer and write every few seconds tons off stuff instead of a constant stream?

Well I have to record a periodic signal.I thought to record a kind of an average of the periods,by measuring first point from first period from the graph,next point from second period…and so on,until I record an entire period from many periods.just theory…