Can't see changes after uploading

I've got a client who uses DW4 and who's website is frames based. Each time he edits his site and uploads the file, the changes don't appear in IE.

First off, I believed it was because of his frames and inability to refresh, but just now he has changed the site and I can see his new file updates thru IE but he can't see the changes.

Could it be that he is now on a Linux server and before becoming my client was hosting on a Windows server? (Clutching at straws here, but I'm at the stage where anything is worth mentioning.)

He has also told me that if he edits from his laptop, no problems it works fine, but from his desktop (a Mac), there is always this editing problem. (This makes me think it's the Mac, but again I could be way off.)

Any suggestions would be muchly appreciated. Thanx.