That's an odd error- I'd recommend you contact ArenaNet about it at their support site: http://support.guildwars.com
Hopefully they'll be able to get things straightened out. If not, you can download the client application from their website and it will automatically download the game for you- you'll have a considerable amount of downloading to do for a while, but you'll at least be able to play.
The Sys. Req. say that ME is supported, so that shouldn't be the problem.
Sounds to me like your setup.exe file is corrupted. You should take the CD back to the shop and ask them to replace it.
I am not saying you have one, but you may want to check for virus'es if you find that a reinstall does not work. You may also need to run scandisk. Hope we can get you ready to play
Thanks for the nice compliment. I presume you got it working; Thats great! Could you post what exactly fixed it? Or did you simply follow all of the steps at the link? It may help others in the future to know exactly what fixed it for you.