Hi leschem,
If you are just wanting to do this on your computer you can do it by setting your macro security level to low (Tools > Macro > Security > set Low option). Unfortunately this will cause macros in all workbooks you open to be automatically enabled, which makes you vulnerable to macro viruses. If you want more security by making this to apply to your workbook but not others you must get a Digital Certificate for your workbook that identifies it as being from a "trusted" source, and set your security level to Medium.
If you want your macros to be automatically enabled with others open your workbook, you are out of luck. After all, this is what macro security is all about--never automatically enabling a macro until the user identifies it as coming from a trusted source. The best you can do in this case is to force the user to enable macros in order for your workbook to be usable. If you want to know more about this, reply back.