Found this article on LifeHacker ( How to Root the HTC Inspire 4G )

HTC Inspire 4G users are lucky enough to have a simple rooting program. With just a few clicks, you should be able to get root access in a snap. To root the Inspire, you'll need the Advanced Ace Hack Kit. After reading all the instructions on that post (they're very persistent about this—I assume because the process can be finicky), download the program and check the manual. Some phones, depending on what version of the HBOOT bootloader they're running, may be wiped during the process, so make sure you don't have anything important on your device. Then, just follow the instructions in the manual. The program itself is dead simple; just pick option 1 at startup and—if you've read the manual and set up all the prerequisites correctly—you should have root access. From there, you can install ROM Manager from the Market, use that to flash ClockworkMod, and then flash any custom ROMs you desire.