Hello Stephane,
This is John from India.
I have been working with the AT89C51, 52 for years and found the most practical method is to use a zif socket soldered to a 40 pin machined base and insert it in the target micro board and then you can program the device with a seperate programmer insert it in your target and test it, this can be done a number of times till your code is working.
(now a days you will be able to get a good free device programming circuit from the net)

You might think this method is tedious, but I have a full fleged 8052 emulator lying with me idle which was more trouble sum to use.

I have also used a an 80C535 from Siemens to emulate these 51/52 micros. Elektor had a eprom emulator board and a 80C535 board which I combined and used it to emulate the micros.
Regards,
John.