Have you tied selecting letter size as the printer page in the page set up from within the Print dilog?
Other than that
1. Quit Illustrator.
2. Rename the AIPrefs file (for example, to AIPrefs.old) in the Users/(user)/AppData/Roaming/Adobe/Adobe Illustrator CS3 Settings folder.
3. Start Illustrator. Illustrator creates a new preferences file.
Also it would nice to know something about your system and hardware and general set up
In the Print dialog you can specify a Media Size or you can choose "Defined by Driver" which is the default. This setting means that the printer driver determines the media size. If you are using Defined by Driver and having a problem then try specifying the media size in Illustrator instead. If you are not using Defined by Driver and having this problem, then try using it.
There are many variables that come into play in any print workflow unfortunately.
Looks like "Pages Per Sheet" option in printer driver is set to more than 1, some times this option is set to more than one if booklet option is turned on in the printer driver options. As these options are applied in the actual printer and can vary based on different printer drivers, Illustrator cannot show the exact preview of final output.
To correct this issue, In Illustrator print dialog, there is an option to access printer driver settings "Setup" in Win and "Printer" in Mac (appearance of the printer driver options vary depending on the drivers), that would take you to the printer driver option where "Pages per sheet" can be set to 1.
If the above doesn't work for you, provide details like platform, printer model, screen shots of printer driver options etc.