You could use Application.ScreenUpdating=False so things happen in the background and set it back to True when done. You could record the macro and get the code for SaveAs. The only thing you might have to worry about is how you want things to be controlled; meaning I'm not familiar with .DBF but I guess it saves only the active sheet. If you're Saving As, you've "lost" the worksheet that the macro was running from unless it's a 'master' file and opens up another sheet and performs save as on it. There is a function SaveCopyAs but I've only used it once. I don't know if it will also save as a different type, it might just be .xls with a different name without affecting the current worksheet.
I'm sure someone else has a better explanation for the control flow.