It's a price heard from a friend-of-a-friend so may be totally wrong but it was about £400.

It would give it a 100Mbit/s interface but you won't get anywhere near that speed. The IDE interface in the empeg uses PIO which limits it to under 1MB/s. You may get a little increase by going to 100Mbit/s ethernet but you won't get 10x the speed.