No problem. This won't work of course unless you happen to be your own Exchange admin. The vast majority of Outlook Anywhere (rpc over http in the 2003 world) installations are set up with Basic auth (at least the ones I know of) and mine always has been as well. Luckily most of our clients are connected directly inside citrix sessions, so this change only affected a few of us.
Client side you simply change from basic auth to NTLM.
Server side you need to open up the EMC, go to CAS configuration, right-click on the server and go to properties. On the Outlook Anywhere tab, change it to NTLM instead of Basic. I then read after googling that you have to manually enable Windows auth on the RPC directory within IIS (not sure if EMC would have eventually propogated this on its own or not, but I did it manually). That got it working, but it would prompt 3 times for auth, wait a while, then prompt 3 more times, etc etc. After more googling I came across a note that by default IIS7 does "kernel-mode" for windows auth (google "outlook anywhere kernel" and you should find it), and there is a command you have to run to disable that. Then restart IIS and it's good to go.
Hope that helps!