keyboard repetition

I have kde 4 on ubuntu 8.04 and I would like to know how to make the repetition of the keys slowlyer and also to make the repetition start later. I found just how to prevent double pressions or to have the character if I keep hold the key for a long time but tidese 2 function are useless for me.
I think I should modify the XFree86 or the XFree98 or the xorg.conf .
I'm a newby so I ask you precise instruction also because I'm almost blind and I make efforts to read.
So I would be pleased if you don't tell me to read the manual or the documentation.
If you could do so I would be very gratefull.
I apologize for my bad English, hope to have made of understood and thank you for the attention.
Best regards
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Guido Nasi