Internet Explorer not rendering well

Morning

I have a Vostro desktop using Vista. My internet exploere is 7 i think. Some sites are not rendering very well in my browser, sadly one of those sites is my new business which is off putting. It's not all the pages just a few bits falling off or overlapping. On other sites however sometimes it is illegible. My site works really well on other peoples versions and also on other settings like firefox. I am so not technical but if anyone has some suggestions or knows how to fix this I'd be very gratefull.

Thanks

Cool bananas

Martin