This probably seems a silly question, but I'm new to iTunes. I'm just wondering if I need to take into account exchange rates while I'm overseas I'f I download books or movie or if because I'm using my pre organized account am I charged as stated?
Any help appreciated.

You get charged at whatever the price and currency is for your itunes account. So for a US account its dollars and for a UK account its GBP. It doesn't matter where you are in the world only what your itunes account is.

People take advantage of this fact by having multiple accounts (UK and US for example) because not all the itunes stores have the same content.

I have a New Zealand account and a US account. I get charged in NZ dollars if I purchase from the NZ account here in the US. It would be the same with the US account if I went back home on vacation.

Thanks for your help everyone. Cheers