8051 uses multiplexed address/data bus so you will have to use 74LS373 or similar to latch the lower 8 address lines.
Example on how to do this you can find here:
**broken link removed**
You can use another external ROM/EPROM and write a short program to erase the EEProm, which,as in the above example, can be connected in the same way to the system as first EPROM + , say, pin P1.0 to select which of them should be used to read program.
Try "software chip erase" option from the Atmel website:
h**p://www.atmel-grenoble.com/dyn/products/app_notes.asp?family_id=638&part_id=1904
Regards,
IanP