Open you part/assembly templates and set the units. Now save them and next time you make new parts, the units would be Inches.
Please note that Deepak is correct on how to fix your existing templates so new documents use your desired units (or any other settings for that matter).
Note that the first time you ever start up SolidWorks, no templates actually exist (they are created the first time you go to the File, New dialog). If no templates exist, it doesn't know what units or drafting standard you want to use so it prompts you to select the units and standard and then writes it to the registry so it will know in the future what to use if it ever has to create templates. So, perhaps you just accepted this dialog with whatever defaults were there and this is why your templates are not currently set up as desired.
Hi Deepak and Jim,
Thanks a lot to both of you for the help. At first, I had a problem saving the modified .prtdot template due to lack of administrative permission. I placed the modified template to another folder and I am now happy camper.
Do you want to change the units on existing files without opening them and doing it individually? If so a macro may be able to do that but I'm pretty sure there's no other way. You might need to move this discussion to the API section.
I want to open new files in English measurement system. I will try Deepak's solution and see how it works. Thank you.