Sharing Outlook Contacts and Calendar

I manage the IT for a small consulting firm (17 employees). All of our machines are either W2K or WXP. Our server is a Server2k box. We use Office 2000 throughout the company. Our email is POP3 supported through our T1 provider. We have been using net folders to share an Outlook contact and calendar database from an older desktop setup in the server room. Net folders recently started flaking out and is now not working at all (yes I know MS no longer supports this program). I am looking for a viable cost effective alternative to installing a MS Exchange server. We do not travel so I don’t need an internet solution but prefer an inhouse software solution. Does anyone have any experience good or bad with the plethora of offerings on the market?