Thats pretty poor. I'm sure I get more life out of mine. If I "reboot" the phone so all the services and apps are running I struggle to get 24hrs of life out of it. Thats with a bit of browsing and a few short calls and sms's thrown in. If I regularly kill the apps with ATK then the life and resposiveness of the phone is improved, 2 days.
Killing the data connection will make a big difference to battery life but I use the connection so frequently it would really hamper the usefulness of the phone. It's a necessity when out an about on holiday though! Has anyone seen a Data "toggle widget" like the Wi-fi, GPS and bluetooth?
If you press the plus button on the bottom right of the home screen, and go to HTC Widgets, then settings, there's a button for mobile network. That controls the mobile data, and should do the job. It doesn't turn of the network altogether, you'll still get calls and stuff.