.ost .pst issues...

[SLCToph]

We have five computers in our office. All but one are syncing the calendar in outlook just fine, back and forth, as is a mobile device. Each of these machines uses .ost data files. The one computer that isn't syncing with the rest is using .pst files. I've tried to change it over, but when I go to add a new data file, it only gives me two options, both of which are .pst. From what I've read, this format can't support syncing for updating the calendar through our microsoft exchange account. And solutions or ideas?