Mac connections to RRAS are slow

I have a Windows 2003 server running Routing and Remote Access, DNS,
and DHCP as an Internet gateway router, domain controller, and file
server. When I use it to access the Internet from a Windows-based
client, I have no problems - pages load instantaneously. However, any
Macintosh clients that I have tried have a ~5-second delay before any
non-cached page will load. Is there a setting that I need to change on
either the Windows server or the Mac client that would make pages load
normally on the Macs? My Internet connection is definitely not the
issue here.

Any help would be appreciated.

Thanks!
Brendan