The product of choice for this type of conversion seems to be the cisco router. If you want to translate HP 802.3 to Ethernet on the same cable, you can configure the cisco to do that. It's been in the product for three or four years. 802.3 to Ethernet was one of their original design goals.
If you want or need a bridge, HP bridges work fine with both Ethernet and HP 802.3 encapsulation. For more details, search the Technical Info library under "cisco."