1904 Date System

Argghhh, I've just finished off flexi-time sheets for several of our departments containing a myriad of formulas to correctly display negative times, when I find I could have used the 1904 date system to do it much more easily.

Before I go and re-do all the sheets, though, I have a couple of questions-

1. If I check 1904 in the options, will it stay checked when used by other people on different PC's (ie it won't revert back to the 'normal' date system)?

2. Will checking 1904 change other people's settings when using other 'normal' Excel sheets (ie will these sheets be changed to 1904, also)?

Thanks for any help you can offer. Bloody Excel :).