Are you sure? This is what I read from Intel Desktop Board DP965LT Technical Product Specification, page 74:
3.8 Boot Options
In the BIOS Setup program, the user can choose to boot from a diskette drive, hard drives, a USB drive, CD-ROM, or the network. The default setting is for the diskette drive to be the first boot device, the hard drive second, and the ATAPI CD-ROM third. If enabled, the last default boot device is the network.
My mistake. Have you tried checking if Legacy USB is enabled?