First Website, issues with allignment

[mintsauce]

Hey there, ive just finished making my first website, and everything works fine on my laptop, ive checked my site in IE, Safari and Firefox. However on my friends pc, the allignment gets all messed up. I cant work out whether this is due to the fact that he has a much bigger screen (22" i think) or if its because hes running off IE 6. It also messes the allignment up when viewed on a mobile phone.

The website address is www.electricalservicescardiff.com

I would be very grateful of any help, as this is my first proper site, and i dont have any coding or webdesign experience, im totally lost with it all!
Thanks in advance