Will canon 480 eg flash for a 35mm camera work on the digital rebel xti?

Yes, but with some limitations.

The Canon 480EG was designed as a TTL flash (through the lens metering) but also has an External Auto metering Mode.

It can be used with any camera that has a PC sync connection. Don't use the "Shoe Cord E" that comes with the flash unless you are using a Film Camera with TTL flash metering.

It can be used with Digital cameras provided you use a PC sync cord to connect the flash to the camera. Use the camera in manual mode and match the settings that you want to use with the flash.