cox regression and change

I'm no statistician, but a porgrammeur. I have some statistics during my study, but is not really one of my stektste points.
'm Trying to calculate things with SPSS, clemintine

I have the following problem. I need to provide the probability of an event happening in the near future.
I know how often the event happend in the past has occurred, with each item. How long ago the event per item last occurred. How often the average time between events occurs in an item.
One of the parameters that influence the county where the item resides. There are a few other factors that having an influence.

I think it seems a bit like determining the cruchtime using Cox regression.
But I do not know if I have to use since the last time the event happend or the average time between events as the survival time .

With the result, I derive a formula that calculated the probability for each item that the event will occurs in the next few months.

In a very compact manual I read somewhere that I have to derive a weighting factor and an index, for by example the Countries and the onter factors
But I have no idea how the outcome of this cox regression translate in the calculations I have to derive.

Can anyone help me?