Different length of the MSI file in XP X Vista

Somebody knows why the length of the MSI file generated in Windows Vista is bigger that the generated in Windows XP? When I compiled my system in Windows XP, the length is 7Mb. But, when I compiled it in the Windows Vista, the size goes up to 15Mb.
I verified all options in the "Tools/Options…", and have the same choices in the two environments.

It is very important for me reduce de length of MSI file because send it attached an e-mail, and my client have a limit of 12Mb per file.

Thanks,

Welcome to the Forums.

This link should help a bit and it also shows how to reduce the msi file size.

http://msdn2.microsoft.com/en-us/library/aa371150.aspx