Yes you can if you root it and download the Barnacle wifi tethering app. I was scared to root my phone but after looking up some info on it, I downloaded universal androot and it basically worked right away. My friend has the Desire and while i like it and its much faster than my phone, I like mine for some of the other benefits it has like the physical keyboard, basically stock android, etc.
Installing a custom rom was much more difficult than rooting and I got it done, but now I'm facing reinstalling the stock rom and unrooting to get the 2.2 update when it comes.