Is there a way to enable WiFi-tethering without root access?

You can get unrevoked, its an app which gives you root access without changing your kernel/flashing a rom/voiding your warrenty, use that on every startup (its automatic) and then get the superuser app. Then you can use the Open Tethering app which requires root access.

Thats the ONLY free way to do wifi tethering. Otherwise pay sprint or your provider the monthly enable tethering fee.

Worst Case Scenario you can tether using EasyTether app. It creates a forwarding mechanism for HTTP requests through the USB port. Requires software on android + computer. Its not WiFi Tethering, but its free, rootless tethering. For 3 bucks you can get the pro version and do HTTPS as well. Better than nothing (or 30 bucks a month --err thats insane--)

My samsung galaxy s (android 2.1) had a tethering option build in from the start. Settings->wifi-Mobile AP and I only had to check a checkbox for it to work. And it works really great. (not locked here t-mobile/netherlands)

I can't find the application name though.

Easy tether is an awesome app that allows wifi tethering. http://www.androidzoom.com/android_applications/communication/easytether-lite_eoqh.html

You won't like this answer but your carrier may provide the service if you're willing to pay extra for it. Sprint offered a WiFi hotspot feature for $30/month on the Evo pre 2.2. Ridiculous, yes. But may be your only option.

I don't know of any way to do wifi tethering without root (before 2.2). You can, however, use bluetooth or a USB cable with PDANet which does not require root.